Axel Jacobs
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1. Figure 23 Light from the sky needs one more bounce than sun light But we also see a cheat that Radiance does In order to reduce its workload ambient sample rays are not sent out for every pixel It is assumed that the ambient light does 3Update Nov 2006 Creating this particular result is no longer possible under Radiance version 3 7 or higher The minimum number of ambient division ad is now set to 27 or 3 if ab is set to zero I left this image here because it shows rather well what happens during the ambient calculation 30 4 HOW RADIANCE WORKS not change a lot throughout the scene which is usually correct Every point for which the ambient light did get sampled carries a sphere of influence As long as a new pixel lies within a radius R of this sphere a new ambient sampling is not carried out Instead the values of adjacent sampling points are interpolated The radius of the sphere of influence is maxSize X aa Rmin _ _ 6 ar MaxSize is the maximum scene dimension as returned by getbbox aa and ar refer the settings for aa and ar which control the ambient accuracy and the ambient resolution resp Increase the ambient divisions to 64 and see what this results in Does it look like Fig 24 Figure 24 The room with one ambient bounce In order to make the scene look less patchy two approaches can be taken e Greatly increase the setting for ad e Get Radiance to sample o2. groundglow source ground 0 0 4 00 1 180 A 6 5 lux plt include line plt title Working Plane Illuminance xlabel Y Position meters ylabel Illuminance lux Adata results lux csv Acolor 2 52 Index 12 defaults 28 36 41 ambient accuracy 31 32 ambient bounces 28 32 39 ambient calculation 28 ambient divisions 31 32 ambient light 29 ambient parameter 32 ambient resolution 31 32 ambient sampling 30 ambient super samples 32 ASCII 10 auto whitebalance 20 back face visibility 14 bgraph 37 39 brightfunc 20 BRTDfunc 18 bubble 13 bulb 21 Cartesian co ordinate system 10 CIE overcast sky 22 colorfunc 20 colour adaptiation 20 colour picker 19 coloured lamps 17 concrete 18 convert 26 daylighting 20 detail 42 dielectric 18 direct calculations 28 dirt 20 distribution 21 dynamic range 26 East 13 enclosing box 14 exposure 18 25 28 29 fabric 18 falsecolor 34 fisheye view 22 front end 42 genbox 14 generator 12 15 gensky 21 getbbox 14 23 31 GIF 27 GIMP 19 glow 20 22 28 graphical user interface 42 ground 19 ground ambient level 22 GUI 42 highlights 18 horizontal illuminance 37 identifier 10 illum 20 28 ImageMagick 26 indirect calculation 30 indoor 29 interactive preview 17 JALOXA 19 lamp tab 20 lampcolor 20 legend 34 light 17 20 28 light bulb 17 luminous efficacy
3. e Added nicer front page and page headers Axel Jacobs Radiance Tutorial e Put all images into floats and gave them captions e Added reference to Colour Picker on LUXAL e Corrected a few typos here and there 6 June 2006 e More explanation on using rcalc in 5 2 18 Feb 2005 e Added 4 2 Ambient Parameters which is essentially copied from rpict options e Added rule of thumb for setting an appropriate av based on exposure e Increased font size to 11pt for better readability 19 Dec 2004 e Added this revision history e Added chapter 3 Previews Visualisation and Image Conversion e Changed all reference from rview to rvu e Included examples for textures and patterns in 2 1 General Information and Syn tax e Updated the listing of the ambient default settings for rvu in 4 1 Ambient Calcu lations to reflect the new settings in Radiance 3 6 e Scrambled author s email addresses on front page to block email harvesters CONTENTS About the Use of Fonts Several different fonts are used throughout this document to improve its readability typewriter commands file listings command lines console output italics paths and file names sans serif Radiance primitives modifiers identifiers Suggested Reading There are number of different Radiance study guides and tutorials available with LEARNIX 3 Figure 1 illustrates the optimal work flow that will give you the best understanding in the shortest amount of time U
4. 3n xi y1 z1 x2 y2 z2 xn yn zn modifier cylinder identifier 0 0 7 x0 yO z0 x1 y1 z1 radius modifier cone identifier 0 0 7 x0 yO z0 x1 y1 z1 radiusO radiusi modifier ring identifier 0 0 8 xyz dx dy dz inner_radius outer_radius A 2 Suggested File Name Extensions 45 Under UNIX it is not necessary to stick to certain file extensions However it is highly recommended to always use the same extensions This will help you stay organised even in directories that contain a large number of files Axel Jacobs Radiance Tutorial File Type Extension scene description rad material definition mat octree oct view file Uf project file rif image file hdr rcalc file cal ambient file amb data table dat plot file plt points file pts BASH shell script bash A 3 Suggested Project Directory Structure When working on larger projects with many differenct input files and results you will very likely notice that keeping an overview of all the different files and versions quickly turns into a challenge While this is not so important for the exercises during the Radiance course or for your assessment you might want to adapt a structured file hierarchy for your projects Here is my personal recommendation ambient Ambient files amb Such files can grow rather large and should therefore be deleted once a project is finished model if the geometry was modelled in a CAD
5. s machines It did not make sense to run processing intensive applications such as ray tracers on desktop PCs Most serious workstations operated under UNIX which provides a multitasking environment It is the UNIX philosophy to have very modular software This is in stark contrast to the concept that MS Windows and the Mac OS follow They aim to provide GUI based software packages that do everything the average user could possibly ask for and a lot more The drawback with this is that the software can only do what its designers had in mind when they programmed it Radiance in contrast consists of more than 100 individual programs This makes it extremely flexible By defining options and chaining together two or more programs a maximum flexibility can be achieved Unfortunately it also means that a steep learning curve is the price to pay Please refer to the separate UNIX for Radiance document for an introduction to UNIX and use of the command line 5 It is essential that you study Chapter 1 of that document before proceeding further o Axel Jacobs Radiance Tutorial 2 Describing a Scene in Radiance 2 1 General Information and Syntax Radiance uses a Cartesian rectilinear coordinate system All information is stored in ASCII text format so it can be edited with any text editor Please refer to appendix A 2 for some commonly used file name extensions There are 4 basic types of primitives Geometry source sphere b
6. The rays need to be specified in the following format xorg yorig zorig xdir ydir zdir Technically it is possible to create entire images with rtrace Because it is usually only used for individual rays the rendering parameters default to more accurate settings Check rtrace defaults to find out more 5 2 1 Getting an Illuminance Reading In a first step we will use rtrace to find out the horizontal illuminance that is created by our overcast sky Since we re only passing the one ray we do this from the command line rather than through a file The UNIX echo command will do the job it sends its arguments to STDOUT Make sure the file sky oct only contains the description and the material of a 10 000 lx overcast sky echo 0 0 0 00 1 rtrace I ab 1 sky oct Radiance oconv skies sky_10klx mat skies sky rad rtrace I ab 1 SOFTWARE Radiance 3 8 lastmod Sun Nov 11 17 10 54 GMT 2007 by root on birdie CAPDATE 2007 12 15 08 52 17 FORMAT ascii 5 594485e 01 5 594485e 01 5 594485e 01 36 5 ANALYSING SCENES octree rpict i luminance image Exposure adjustment of background exposure adjusted luminance image falsecolor cl i p 1 1ux Y falsecolor cl i 7 p 7 1 1ux false colour illuminance image Figure 28 Flowchart for creating false colour images of the pixel illuminance The first eight lines of the output are the header which can be disabled with the h
7. monitor or printer This is done with the pfilt command rpict vp 10 10 10 vd 1 1 98 vh 5 vv 5 e 1 ab 1 chair oct gt images chair_rpict hdr pfilt e 5 images chair_rpict hdr gt images chair_rpict_pfilt hdr ximage images chair_rpict_pfilt hdr 3 3 Image Conversion Radiance comes with tools for converting images from the special Radiance RGBE format other formats All such converters start with ra_ in their name for example 25 Axel Jacobs Radiance Tutorial ra_tiff will convert the Radiance RGBE format to a TIFF The TIFF format is un derstood by virtually all image processing software but results in rather large file sizes It might therefore be a good idea to convert from TIFF to a file format which results in smaller files The PNG pronounce ping format is ideally suited for this Although ImageMagick is not part of the Radiance distribution it is installed on many UNIX and LINUX systems and also on LEARNIX ImageMagick 1 provides a number of programs for displaying and manipulating image files The convert command uses the file extension to decide what format to export to cd images pfilt e 1 chair_rpict hdr gt chair_rpict_pfilt hdr ra_tiff chair_rpict_pfilt hdr chair_rpict_pfilt tif convert chair_rpict_pfilt tif chair_rpict_pfilt png rm chair_rpict_pfilt tif cd All of the above assumes that the Radiance image file has a proper exposure set using the pfil
8. A2 3 Pz A2 3 mx Sqrt diri my Sqrt 1 abs diri mz Sqrt diri xwrink Rdot A1 A3 mx fnoise3 Px A3 Py A2 Pz A2 ywrink Rdot A1 A3 my fnoise3 Px A2 Py A3 Pz A2 zwrink Rdot A1 A3 mz fnoise3 Py A2 Py A2 Pz A3 48 A APPENDICES A 6 File Listings A 6 1 objects chair rad This is a very simple chair Dimensions are in metres It is 0 5 m high back 1 0 m and 0 4 by 0 4 m wide The centre is at 0 0 void plastic chairmat 0 0 5 2 2 1 00 void plastic fabric 0 0 5 8 4 2 00 Igenbox fabric seat 5 5 05 xform t 25 25 45 Igenbox fabric back 05 5 3 xform t 2 25 7 chairmat cylinder legi 0 0 T 225 2250 225 225 9 025 chairmat sphere knob1 0 0 4 225 025 9 025 chairmat cylinder leg2 0 0 7 225 225 0 225 225 45 025 chairmat cylinder leg3 0 0 T 225 225 0 225 225 9 025 chairmat sphere knob3 0 0 4 225 225 9 025 chairmat cylinder leg4 0 O 49 Axel Jacobs Radiance Tutorial 7 225 225 0 225 225 45 025 A 6 2 objects table rad This is a very simple table Dimensions are in metres It is 0 85 m high and 1 by 1 m wide The centre is at 0 0 void plastic tablemat 0 0 5 5 3 1 00 Igenbox tablemat tabletop 1 1 05 xform t 5 5 8 tablemat cylinder legi 0 0 7 4 4 0 4 4 8 025 tablemat cylinder leg2 0 0 7 4 40 4 4 8 025 table
9. Converters are available that allow us to export from a limited number of commonly used 3D file formats to Radiance Such converters might be plug ins to the relevant software package as is the case with the su2rad plug in for Sketchup 12 Others are command line applications Examples include converters for the 3DS OBJ and DXF formats If you decide to use a CAD package for doing the modelling you should be aware that objects can be modelled in different ways A box for instance may be modelled as 1 The six surfaces if the box This is a surface model 2 The volume contained by the box A solid model Only surface models are suited for use in Radiance See Fig 7 A well written translator might be able to convert volume models into surface models because all the necessary information is contained within the model When in doubt consult the documentation of your CAD software Most CAD modellers will only export objects of type polygon This is fine Polygons are by far the most frequently used type of geometry Just be aware that once a polygon is defined you can t later cut a hole in it e g to put in a window If this is what you need to do there are several options to your disposal Some obvious and useful ones 12 2 DESCRIBING A SCENE IN RADIANCE a Surface model b Solid model Figure 7 Only surface models can be imported into Radiance are depicted in Fig 8 It s usually best to split up the larger polygon
10. and objects chair rad respectively Use getbbox and objline to see whether you H get the desired result i Il ts ll gt a a A chair viewed with b Four chairs around the table objline Figure 12 Arranging the furniture objline is somewhat unusual in the sense that is produces X11 meta files This is a special vector format that looks like garbage when output to the terminal To render the image we need to pipe it into x11meta like so objline objects chair rad xiimeta We will later on meet another program that works in tandem with xiimeta bgraph 6 Create a file objects bulb rad which describes the geometry and the material for You would be right in saying that furniture rad should sit in the objects subdirectory Unfor tunately objline and objview don t parse nested in line calls to xform the same way and it is safer if furniture rad remains in the root of our project directory 2You shouldn t really call this thing a bulb In the vocabulary of a lighting engineer a bulb is something you plant in your garden A lamp is the thing inside a luminaire that generates the light which the luminaire shapes and models An example for a lamp would be a tungsten halogen reflector lamp an example for a luminaire could be that thing on your desk that looks very stylish throws really bad light and has a lamp inside 16 2 DESCRIBING A SCENE IN RADIANCE the l
11. in a scene e g metal halides and tungsten If you assign a WHITE i e non coloured lamp type to all your light sources you can colour balance the white point of the final rendering with the pfilt command at a later stage A list of available lamp types can be found in lamp tab On our LEARNIX system this file resides under usr share radiance A normal tungsten lamp has a luminous efficacy of around 15 Im W We assume a 100 W lamp lampcolor Program to compute lamp radiance Enter for help Enter lamp type WHITE incandescent Enter length unit meter meter Enter lamp geometry polygon sphere Sphere radius 1 03 If you have compiled Radiance yourself it will be in usr local lib ray 20 2 DESCRIBING A SCENE IN RADIANCE Enter total lamp lumens 0 1500 Lamp color RGB 235 85 235 85 235 85 TC These values need to be given as real arguments to the material primitive defining the material of the bulb Use the material light 2 3 4 Daylight Descriptions of daylight are generated with the gensky command It defines the distrit bution of sky and ground radiance It is left to the user to define two hemispheres of type source one for the sky the other for the ground source objects are infinitely far away from any observer and defined by their direction and an angle rather than their absolute x y z coordinates as all other Radiance geometry primitives are It is also left to he user to take c
12. into smaller ones leaving the opening free Figure 8 Cutting a hole into a polygon 2 2 2 Modelling Geometry A Radiance scene should always be aligned so that the x axis points East the y axis points North and the z axis points upwards to the zenith as shown in Fig 9 This is in contrast to some 3D modelling packages which use x and y for the horizontal and vertical dimensions and describe the depth i e the distance behind or in front of the computer screen with the z coordinate Z South Figure 9 The Radiance convention on alignment of the coordiante system follows the right hand rule Sizes and distances can be given in any unit of length as long as they are used consistently throughout the entire project When flicking through the Radiance User Manual 8 you will find that many surface primitives come in two flavors An example is sphere and bubble Both describe a ball shaped object The difference between the two is that a sphere has a surface normal 13 Axel Jacobs Radiance Tutorial that point outwards whereas the normal of a bubble points inwards As long as the bv switch to rpict is set to turn on back face visibility this doesn t really matter for most materials It does matter however for light sources and mirror The different surface orientations also need to be remembered when using the genbox command and other ge
13. s normtiff command and then to JPEG or mogrify gamma 2 2 format png images hdr to convert to PNG with ImageMagick s mogrify convert actually relies on the Radiance ra_ppm to do the work 27 Axel Jacobs Radiance Tutorial 4 How Radiance Works 4 1 Ambient Calculations Compile a new octree and include the following files materials course mat skies sky mat skies sky rad and objects room rad Give it the name scene oct Make sure there is no furniture in the room and that you have an overcast sky in sky mat We now view the octree scene oct with rvu oconv materials course mat skies sky mat skies sky rad objects room rad gt scene oct rvu vf views nice vf scene oct rvu warning no light sources found Figure 20 A black room You will notice that everything inside the room appears black Using the trace command from within rvu check whether this is just a question of poor exposure or if the room really is black Check the default settings for ab and av for rvu rvu defaults grep a av 0 000000 0 000000 0 000000 ambient value aw 0 ambient value weight ab 0 ambient bounces aa 0 300000 ambient accuracy ar 32 ambient resolution ad 256 ambient divisions as 64 ambient super samples Both parameters have 0 as default A value of zero for the number of ambient bounces turns the ambient calculation off So only light sources of type light spotlight or illum will be
14. 20 22 37 meta file 16 meta format 23 metal 18 mirror 14 modifier 10 mogrify 27 normalised 19 normtiff 26 North 13 objline 14 16 23 objpict 23 objview 18 24 oconv 17 octree 17 outdoor 29 53 Axel Jacobs Radiance Tutorial overlay 34 paper 18 patchy 31 pattern 11 19 pfilt 20 25 26 35 pivot 18 plastic 18 PNG 26 PostScript 23 39 primitive 10 psmeta 23 quality 41 rad 41 ra_tiff 26 rcalc 35 rectilinear 10 reflectance 18 19 retina 19 right hand rule 14 rotate 18 roughness 19 rpict 14 17 23 24 41 rtrace 17 36 rvu 17 23 24 41 secondary light source 20 self luminous 20 shadow 29 32 sky 19 skyfunc 22 solid angle 31 solid model 12 source 21 specularity 19 sphere 13 sphere of influence 31 splotch 30 32 spotlight 20 28 STDOUT 17 stochastic sampling 32 surface model 12 surface normal 13 texture 11 19 TIFF 26 trace 18 28 trad 42 transmittance 18 tungsten 20 unit 13 variability 42 vector 23 vector format 16 view 17 void 10 water 11 20 weighted average 19 WHITE 20 white point 20 window 20 wood 11 18 working plane 37 xllmeta 14 16 23 xform 15 ximage 23 35 zenith 13 54
15. Laboratories it has evolved into an extremely powerful package that is capable of producing physically correct results and images that are indistinguishable from real photographs oconv rtrace rvu rpict 4 display A ximage Figure 2 The main components of the Radiance rendering system Its versatility makes Radiance the ideal choice not only for serious researchers but also for architects lighting designers and other professionals Although a challenge to learn Radiance especially in a UNIX environment is capable of producing results that no other visualisation package can achieve 9 1 2 Ray tracing vs Radiosity Radiance employs backward ray tracing algorithms This means that the light rays are traced back from the point of measurement or view to the light source There are a number of other ray tracers on the market because the basic principle is relatively simple to implement on computers However where Radiance stands out is its ability to handle diffuse inter reflections between objects Very efficient algorithms together with caching are applied for this Other packages usually try to equate for indirect contributions by defining the ambient light that has no real source and somehow is everywhere Examples for other ray tracers include POV or 3DStudio Max Because the calculations are started from the view point an entirely new calcula tion has to b
16. NIX for Radiance Chapter 1 NL Radiance Tutorial KT UNIX for Radiance Chapter 2 Difficulty NL Radiance Cookbook SL Understanding rtcontrib Figure 1 You are strongly encouraged to follow this path while studying the LEARNIX documentation You are encouraged to follow this suggestion If you do feel proficient enough to skip certain sections of a particular document or even an entire document you might miss out on some important information that later sections rely upon Simply skipping over parts that you might find boring or otherwise un interesting will leave serious gaps in your understanding of Radiance It is important that you try to understand all exercises and you absolutely MUST do them yourself Don t just flick through the pages and look at the pictures There are other sources of information namely e The man pages 6 e The official Radiance web site 7 e The Radiance mailing list and its archives available through the Radiance com munity web site 10 e The book Rendering with Radiance 9 You may consult them at any time either while studying with the help of the resources on LEARNIX or afterwards Good luck with your efforts e Axel Jacobs Radiance Tutorial 1 Introduction 1 1 What is Radiance Radiance is a sophisticated lighting visualisation system Originally started off as a research project at the Lawrence Berkeley
17. Radiance Tutorial Axel Jacobs lt axel AT jaloxa DOT eu gt Axel Jacobs Radiance Tutorial CONTENTS Contents 1 Introduction 1 1 What is Radiance 1 2 Ray tracing vs Radiosity 1 3 Do it the UNIX Way 2 Describing a Scene in Radiance 2 1 General Information and Syntax 2 2 Describing the Geometry Approaches to Modelling 2 2 2 Modelling Geometry 2 2 3 More Complex Scenes 2 3 Describing the Materials Standard Materials Materials Modified by Patterns and Textures 2 2 1 2 3 1 Dl 2 3 3 2 3 4 3 Previews del 3 1 2 3 2 1 3 2 2 Non interactive Visualisation 3 3 Image Conversion Light Sources Daylight caos e 24 446 64 6 Visualisation and Image Conversion 3 1 Quick Preview of Objects GO LIDE ga popa Soka a a OOIPLCE es p wee on su de 3 2 Visualisation Interactive Visualisation 4 How Radiance Works 4 1 Ambient Calculations 4 2 Ambient Parameters 4 2 1 Useful Ranges 4 2 2 Artifacts Associated with Options 4 2 3 Timings Associated with Options 5 Analysing Scenes 5 1 Analysing Radiance pictures ob 5 1 2 Analysis With ximage 5 2 Analysing Models with rtrace 5 2 1 5 2 2 Plotting luminance Values Creating False Colour Images Getting an Illuminance Reading 6 The Joy of Rendering 6 1 Too Much to Remember 6 2 The rad command 6 3 Being Lazy References 00 00 00 28 De E o he bo e 8 te ate a ate A 28 ge fi ata mt d Oh Au tc ai a d 32 i p
18. are of the colours of sky and ground To start with let s create a sunny sky for London at today s date You should redirect the output to a file called skies sky mat gensky 12 09 14 00 a 51 o 0 m 0 gensky 12 09 14 00 a 51 o O m O Local solar time 14 14 Solar altitude and azimuth 11 0 29 9 Ground ambient level 8 7 void light solar 0 0 3 2 72e 06 2 72e 06 2 72e 06 solar source sun 0 0 4 0 489041 0 851114 0 190903 0 5 void brightfunc skyfunc 2 skybr skybright cal 0 7 1 3 76e 00 3 72e 00 2 98e 01 0 489041 0 851114 0 190903 gensky will only create the distribution of sky and ground as well as the material definition and the actual object for the sun Materials for sky and ground and the two hemispheres are left to the user to define Sun Sky Distribution gensky gt skies sky mat Material gensky gt skies sky mat user gt skies sky rad Geometry gensky gt skies sky mat user gt skies sky rad 21 Axel Jacobs Radiance Tutorial You might notice that the table above is not consistent with our naming conventions to always keep the materials in a mat file and the geometry in a rad file This is because gensky produces materials sky distribution and sun material as well as the sun geometry When defining the material properties care must be taken to use skyfunc as modifier to the material for both the sky and the ground This is already done in the file ski
19. bled with the w switch This should no longer be necessary if you know what you re doing 37 Axel Jacobs Radiance Tutorial 0 85 m Figure 29 Taking illuminance readings already been prepared for you It lists the points of the measurement and the direction vectors as x y z triplets ct un cat data line 0 85 85 85 85 85 85 85 85 85 N D ND D ND ND D N D e sde ee so 5 w amp D ND H H nonononon oooooooo P 0 0 0 0 0 0 0 0 0 O O O OG QT COC ererrrrerrre You can easily see that only the y coordinate differs between the points If you are interested in how such a grid file can be created with Radiance s rcalc command please refer to the chapter titled Dynamic grids with cnt in the Radiance CookbookAxel Jacobs 2 The points are now fed into rtrace cat data line pts rtrace I ab 3 h scene oct Radiance oconv materials course mat skies sky mat skies sky rad objects room rad rtrace SOFTWARE Radiance 3 7 lastmod Sat Nov 18 23 28 38 WET 2006 by FORMAT ascii 6 0374e 00 7 3870e 00 8 5235e 00 3 8192e 00 4 6729e 00 5 3918e 00 1 3492e 00 1 6508e 00 1 9047e 00 38 5 ANALYSING SCENES rtrace will normally only output the value which is in our case the irradiance for the Red Green and Blue channel If run without the I switch this would be the radiance instead This is fine except that plotting is easier if the position of the sensor is printed as
20. by moving the interactive sliders across 1 With its help it s much easier to choose materials as it will also compute the reflectance and normalised colour important for sky and ground for you You can just copy and past the results into your mat file 2 3 2 Materials Modified by Patterns and Textures While defining the materials for plain colours is a straight forward process the scene will look more interesting and real when we apply patterns and textures to the object 19 Axel Jacobs Radiance Tutorial Patterns describe changes in colour while textures refer to perturbations of the surface normal A picture mapped onto a frame hanging on the wall is an example for a pattern Ripples on a body of water on the other hand can be created through textures We can string as many patterns and textures together as we like the sky is the limit How about a dusty wooden table with stains and a chess board laid in and some scribble on it A combination of brightfunc colorpic and texfunc will do the trick materials course mat has two brightfunc and one colorfunc primitives defined for you Create a nice blue stripe across the walls by applying blue_band to wall_mat Additionally use floorpat to put some random tiles on the floor and make them look dirty with dirt Try to understand what each function does 2 3 3 Light Sources The available materials for light sources in Radiance are light illum glow and spotlight light is th
21. cts are uniformly lit without any shadows Figure 21 Our room lit only by ambient light This is almost certainly not what you want This approach does have advantages though For every pixel in the image only one ray needs to be traced making this a quick and dirty solution SThis value is in units of W m Radiance Digest V3n2 29 Axel Jacobs Radiance Tutorial Before you quit rvu create a plan view of the entire floor and save it as views floor uf The appropriate view type is 1 for a parallel view In order to find out how the indirect calculation affects the quality of the rendering set av back to zero and run rvu with one ambient bounce Additionally set the number of ambient divisions to one with the ad 1 option rvu vf views floor vf av 0 0 0 ab 1 ad 1 scene oct This is now quite a strange looking result Fig 22 The majority of the floor is still black but there are a number of circular splotches that have a bright centre and fade towards their periphery Figure 22 Ugly splotches The ab 1 option that we used here turns the ambient calculations on However only one ambient sample ray is sent off for each position where ambient sampling occurs ad 1 option So the chances of this ray eventually going through the window and hitting the sky are rather small and decrease even more with the distance from the window ab 1
22. cts chair rad After setting up the model including materials objects and light sources the last step before running a proper simulation with rpict is oftentimes to define a nice view This is rather difficult to achieve on the command line but very easily done interactively within rvu 24 3 PREVIEWS VISUALISATION AND IMAGE CONVERSION Figure 18 The chair in rvu oconv skies skyovercast mat skies sky rad objects chair rad gt chair oct rvu vp 10 10 10 vd 1 1 98 vh 5 vv 5 ab 1 chair oct On the rvu command line adjust the exposure and save the image For a list of commands that are available in the rvu shell please refer to the table in section 2 2 3 done e Pick point for exposure w chair_rvu hdr writing chair_rvu hdr v views chair vf done Once you have a good view save the view parameters into a file Make sure it has a uf extension This is not necessary for Radiance to pick it up but makes it a lot easier on you to remember what all those files in your directory are That is also the reason why you are encouraged to store all of your view files in the views directory 3 2 2 Non interactive Visualisation After all these preparations it s finally time to hit the BIG button not that this exists on the command line Most commands in the next section assume that the image has been given a good exposure that makes most of the objects visible within the dynamic range of the display device
23. cy This should result in the diffuse horizontal illuminance which we set to 10 000 lx The sky and ground must both be made of the material glow However glow in contrast to light spotlight and illum does not get sampled during the direct calculation It will only make indirect contributions See section 4 1 for more details 22 3 PREVIEWS VISUALISATION AND IMAGE CONVERSION 3 Previews Visualisation and Image Conversion Radiance objects and scenes can be visualised with a number of different programs Except for objline they are all based on either rvu or rpict and add functionality or convenience through scripts The diagram in Fig 15 attempts to give an overview of the viewers in Radiance and when they can be used The programs on the right hand side are sorted in increasing complexity and image quality from top to bottom Are all materials gt objline xllmeta defined N Are light sources objpict defined objview rpict Figure 15 Different commands are available to view your scene 3 1 Quick Preview of Objects 3 1 1 objline Whilst modelling the geometry of an object or scene it is often useful to get a quick overview of the size and position of objects The objline program is useful for quickly visualising the geometry without having to worry about correct material definitions The software produces the result in meta format which is vector rather than pixel base
24. d To display it on the screen please pipe it through x1imeta objline objects chair rad xiimeta Alternatively an Encapsulated PostScript output can be produced which can then be imported into other documents The evince document viewer that is available on LEARNIX can display the EPS format objline objects chair rad psmeta gt images chair eps Don t forget that there is also the getbbox command which will tell you how big the object is and where it is located 3 1 2 objpict If all materials as well as the geometry of the objects are defined except for the light sources the objpict program can generate a four view image of the objects by taking care of placing some light sources in the scene to make sure the objects are actually visible The output is a Radiance image so don t forget to redirect the output into a hdr file or pipe it into ximage 23 Axel Jacobs Radiance Tutorial e Figure 16 The chair again objpict objects chair rad ximage or objpict objects chair rad gt images chair hdr ximage images chair hdr Figure 17 Previewing the chair with objpict 3 2 Visualisation 3 2 1 Interactive Visualisation If an interactive visualisation with rvu is required but light sources have not been defined yet objview will take a list of material and geometry files compile an octree and call rvu objview obje
25. e basic material for self luminous surfaces It is used for most light emitting objects It s used to model the sun in a clear sky illum is used for secondary light sources with broad distribution i e windows illum sources are treated like ordinary light sources except when looked at directly They then act as if they were made of a different material See section for details glow is for self luminous surfaces that have a limited effect For daylighting it is used for the sky hemisphere as well as for the ground spotlight is used for light sources with a directional output It has little relevance since it gives rather unrealistic results For real spot lights it s much preferrable to use the light material in combination with a data file describing the luminance distribution of the fitting For physically correct results it is important to determine the correct radiance values for the red green and blue channel The lampcolor program does this for us We use the type WHITE here Use this whenever you are rendering a scene that is only lit by one type of light source irrespective of what this may be A mechanism called colour adaptiation causes our brains to automatically adjust to the colour temperature of the predominant light source in a scene This is similar to the auto whitebalance function that is built into digital cameras Choosing a none white lamp type is only recommended if there are different types of lamps
26. e done for each individual view Walk throughs and videos are therefore extremely resource hungry requiring fast computers and a lot of time There is another conceptually different approach to compute light distributions This method is called radiosity Radiosity based algorithms start off with the energy that is radiated from the light source Assuming diffuse reflectance properties of the 1 INTRODUCTION objects the incoming energy is then modified by the material s reflective properties and bounced back into the room This is done until the contribution of the reflected light towards the average illuminance in the scene becomes insignificant The energy distribution of the entire scene is calculated and stored This means that once all the calculations are done new view points can be created in no time at all This makes the radiosity solutions ideal for the creation of virtual worlds such as VRML Scenes created this way can usually be told because of their lack of reflective and transparent surfaces although newer software implements get arounds to these problems A typical example of a simulation package that uses radiosity is VIZ ex Lightscape by AutoDesk 1 3 Do it the UNIX Way The Radiance source code is freely available for download from the Internet Radiance was developed to run on UNIX machines Part of the reason is that in the early 1990s when Greg Ward started writing Radiance computers were very slow compared to today
27. en more than that By setting only three variables for the overall quality the importance of indirect calculations and the level of detail in the scene rad automatically takes care of most of the rpict options that are vital for getting a good quality image The file room rif is set up for the simple test room we have been working with cat room rif Rad Input File DETAIL Low INDIRECT 1 OCTREE room oct PICTURE images room QUALITY Medium RESOLUTION 800 VARIABILITY Low ZONE Interior 04050 3 materials materials course mat materials skies sky_overcast mat scene objects room rad skies sky rad view nice vf views nice vf Options in UPPERCASE can only appear once within the RIF file those in lowercase may be repeated This is the case for the materials option in room rif To call it with rvu you need to give it an output device Type rvu devices to get a list Use x11 for now rad o x11 v nice room rif rvu vu 0 0 1 vf views nice vf ps 6 pt 08 dp 512 ar 20 ms 0 1 ds 3 dt 1 dc 5 dr 1 sj 7 st 1 ab 1 aa 25 ad 196 as O av 0 01 0 01 0 01 lr 6 lw 002 R nice rif o x11 nice oct To run rpict simply drop the o x11 option If you also drop v one image for each view will be rendered Using the example RIF file above the image would be named images room_nice hdr 41 H Axel Jacobs Radiance Tutorial The table below lists the available variables and how they affect renderin
28. es sky rad The photometric average of the radiances according to Eqn 3 must be equal to 1 0 otherwise the light levels will not be correct 1 0 0 265R 0 670G 0 065B 3 Now bring up the result in rvu Set up a nice fisheye view of the sky hemisphere and save the parameters into views fish uf oconv skies sky_overcast mat skies sky rad gt sky oct rvu sky oct When run with the c option the gensky command produces a CIE overcast sky whose absolute brightness and hence the horizontal illuminance that it produces is a function of the solar altitude The actual sun is of course not generated When daylight factors rather than illuminance readings are required it is convenient to work with a 10 000 lx sky This way we can simply divide the illuminance by 100 to get the daylight factor To create a sky that produces a certain horizontal illuminance we run gensky with the B option The a o and m options are not necessary for this B requires the horizontal diffuse irradiance Rhoriz so we need to divide the illuminance Eporiz by Radiance s luminous efficacy Ehoriz Rhoriz 179m w 4 gensky 12 4 12 00 c B 55 866 gt skies sky_10k1x mat Re create the octree again and look at it interactively using the view file from the last exercise Now look in the file skies sky_10klx mat Find the ground ambient level multiply it by 7 illuminance from a hemispherical source and multiply again by 179 luminous effica
29. ext use the genbox command to create a box Append it to objects things rad The general syntax for genbox is 14 2 DESCRIBING A SCENE IN RADIANCE genbox material name xsize ysize zsize Additional options are available such as rounded or chamfered edges Please refer to the genbox man page for details Open objects things rad in a text editor and remove two or three adjacent faces Look at the result with objline Create another box of different dimensions This time don t call it from the com mand line Instead put an extra line in objects things rad that calls the generator Remember to begin the line with We have just explored two different ways of calling generators e The first one creates quite large and cumbersome files but allows us to make modifications to individual parts of the object Unfortunately this is what most converters from CAD packages will produce A perfect cylinder for instance which is very simple to model using a native Radiance primitive will be split up into a number of polygons The result will not look not very nice unless a very large number of polygons is created However this will result in large file sizes e The second way is nice because it is only one line of text that we can easily understand To change the size of the box only requires the alteration of one argument compared to twelve coordinates done the other way The drawback of this method is that only the whole object can be
30. g It is not necessarily the smallest value numerically fast for reasonably fast rendering accur for reasonably accurate rendering artificial lighting very accur for accurate rendering or complicated scenes daylighting max for the ultimate in accuracy Avoid using the max setting for aa and ar This disables optimisation and can be very expensive in terms of rendering time 4 2 2 Artifacts Associated with Options Parameter Artifact Solution ab lighting in shadows too flat increment value av overall light level seems too high low decrease increase value aa uneven shading boundaries in shadows decrease value by 25 ar shading wrong in some areas double or quadruple value ad splotches of light double value as splotches of light increase to half of ad setting 32 4 HOW RADIANCE WORKS 4 2 3 Timings Associated with Options Parameter Effect on Execution Time ab doubling this value can double rendering time aa doubling this value approximately quadruples rendering time ar effect depends on scene can quadruple time for double value ad doubling value may double rendering time as effectively adds to ad parameter and its cost 33 Axel Jacobs Radiance Tutorial 5 Analysing Scenes 5 1 Analysing Radiance pictures 5 1 1 Creating False Colour Images The falsecolor command allows us to create looking false colour images which map the luminance or illuminance val
31. g times and quality They are listed in order of most to least important to rendering time For instance increasing QUALITY from low to high will increase the rendering time by a factor of 25 while doing the same for DETAIL will only result in the simulation taking 10 times as long The multipliers are relative to the low setting within the same row Please compare to table 12 1 in 9 affected parame low medium high ters b 0 as 0 b INDIRECT Ras QUAL most a 7 74 a INDIRECT xl aa xl ar x2 aa x0 8 ar x4 aa x0 6 VAR ad aa ad x1 aa x1 ad x2 aa x0 7 aa x0 3 ad x2 DET ar ar x1 ar x2 ar x4 6 3 Being Lazy As if all this wasn t enough there is even a graphical user interface GUI with Radi ance It is called trad trad is a front end for the rad command It doesn t need any explanation Just try it out It comes with a help system that will happily answer all your questions trad amp Jhome axel projects radiance tutorial basic radfiles tutorial jroom rif ZONE e Interior C Exterior FILE Maximum 4 s 3 C SCENE Auto X Y Z e ZONE Minimum jo o CE C VIEWS Detail C High Medium Low gis C ACTION Indirect 1 C RESULTS EET HELP Variability High Medium Low QUIT Exposure _ Copy Revert Figure 31 trad is a graphical interface to the Radiance rad command 42 REFERENCES References 10 11 12 ImageMagick URL htt
32. ie o ae Mh Bo AD a ea aaa Gee a 32 y prp Sede m ec ee eee 32 o ec Bog Ae Be BMA a re student 33 34 Dad s ee GR otek SAMs A oe ae c t d af 34 sive ake det tas alea te aha i gg ere 34 a Ke he A al e A Bote Sok wes 35 a s de Reve ee ee Gece de aes See Aaa e 36 ie EG A oe een Be aa ant es 36 Syn e ie e a Go 37 41 ue Gee ee A ee oe Rd etes 41 a ra 41 i RE de al 42 43 Axel Jacobs Radiance Tutorial A Appendices 44 A 1 The Main Primitives and Their Parameters 44 A 1 1 Materials 44 ALD a eos ee ou ui US NA UN hi Ma RL same 44 A 2 Suggested File Name Extensions 45 A 3 Suggested Project Directory Structure 46 A 4 Files Used in the Course 47 A 5 Material files for the pattern and texture example 47 Aod WOBIMB cias ra Bae ee ae a ee Se De 47 AOD wood pata ss oe ae ee alt ca a ala A 47 AGS AUGER GRRE ead cae ao rai Lars See e a ee a da aia ed 48 ASA urinklecal ss kan e de eR e da RR mE rata 48 AG Pile Listes L eR A RR A n d a 49 AGI DE CNAE dee pe m ea e a RHE RA eee a 49 AGOJ a Le be eee se re d ler e e bd bee Ow d 50 A63 maker seourse MaE Le eee be m SE ee es 50 AGA ENERGIA roere ee e Oe ede SSS ic d re adi d 51 AGS JUMQ sc 2 4 su sa Sed Phe a wee Lee eee ER ee Es 52 CONTENTS Revision History 23 Jan 2012 e Fixed minor inconsistenc
33. ies e Reflect changes in Radiance 4 1 Dec 2011 rpict w and Radiance HEAD Jan 2012 falsecolor 19 Dec 2010 e Fixed a few inconsistencies 2 Apr 2010 e Moved section Secondary Light Sources to the Cookbook I haven t found the time to cover it for about five years e Derived a simplified formula for the transmissivity in Appendix A 1 1 but put all the explanations in the Cookbook e Some tidying up 25 Oct 2008 e Decided to eat my own dog food and be consistend with the recommended file structure and naming conventions as laid out in A 3 e Some tidying up 26 May 2008 e Added suggested directory structure for projects to the appendix e Fixed a type with the transmittance formula in the appendid and added a graph e Moved the Introduction to UNIX to a separate document Change tables to the more formal tabular formatting newly introduced in LyX 1 5 e Unified the hand made bibliographies to BibTEX e Added info on gamma correction to image conversion 26 Dec 2006 e Changed the section dealing with illuminance plots so that the measurement points are read in from a file and not generated by cnt Many students find the use of rcalc too confusing and it s not necessary here The old cnt rcalc version is now in the Advanced Tutorial e Updated the falsecolor pages e New section on wild cards e Added index e Updated CAD import and primitives sections e Added margin icons for files in the ZIP archive 10 Nov 2006
34. ight bulb Place the sphere at the origin of the coordinate system and give it a radius of 3 0 cm For now we assume a white light source Use the material light and give it equal values for the red green and blue radiance Please refer to section 2 3 3 for more information on coloured lamps 7 In a file called lights rad us xform commands to place two of your bulbs at a height between 2 5 and 3 0 m Before we catch a first glimpse of the image the scene needs to be compiled into an octree The purpose of an octree is to speed up the calculation by only considering the objects that lay within the path of a ray The command to use is oconv It takes as arguments all material and scene files that we want to include oconv will not compile a scene file unless all materials that are used are defined To make things easier the file materials course mat contains everything that is needed in this exercise The materials have to be given first or oconv will drop out with an error The octree is produced at STDOUT so you will need to redirect it into a file oconv materials course mat objects room rad objects furniture rad objects lights rad gt scene oct There are three commands that accept an octree as an input and trace rays within the scene They all start with r rvu for in interactive preview rpict for producing an image and rtrace to trace a single ray Use rvu for an interactive view of the scene using the view para
35. lette has changed in version 3 8 of Radiance The new palette has more colours in it which makes it easier to interpret 34 5 ANALYSING SCENES falsecolor i images scene_i hdr p images scene hdr cl n 10 s 2000 1 lux gt images false hdr The 1 option sets the label of the legend The result is shown in Fig 26 on the right a Luminance b Illuminance Figure 26 Producing false colour contour lines If you re still not entirely happy with the way that pixel values are represented by falsecolor please feel free to try out alternative colour palettes pal option An HDR image of the available palettes can be generated with the palettes switch Don t forget to pipe this to ximage or to save it to a file You may also want to experiment with the cb or cp options that create contour bands or a posterisation effect resp Understanding the difference between the illuminance and luminance you will ap preciate why the contour lines follow the carpet pattern in the false colour luminance picture but not in the illuminance one When using falsecolor with overlaid contour lines you might have to adjust the exposure of the background image Do this before running pfilt The image from which the values are extracted never needs to have its exposure adjusted Figs 27 and 28 summarise the use of the falsecolor command for luminance and illuminance scales 5 1 2 Analysis With ximage If only a handful of values a
36. mat cylinder leg3 0 0 7 4 4 0 4 4 8 025 tablemat cylinder leg4 0 0 7 4 40 4 4 8 025 A 6 3 materials course mat void brightfunc dusty 4 dirt dirt cal s 1 0 1 4 void brightfunc floorpat 2 4 rand floor Px 25 25 floor Py 25 25 6 0 0 void colorfunc blue_band 4 if Pz 1 2 1 if Pz 1 0 1 if Pz 1 2 1 if Pz 1 0 1 1 0 50 A APPENDICES void plastic wall_mat 0 0 5 7 7 7 00 void plastic ceiling mat 0 0 5 9 9 9 00 void plastic floor_mat 0 0 5 6 5 5 00 Total dirt corrected glazing transm after CIBSE LG10 1999 JALOXA LG10 Glazing Calculator for Radiance http www jaloxa eu resources radiance 1g10_glazing shtml Glazing transmittance A1 5 gt 0 69 Double glazing clear float low E glass Loss of daylight compared with clean glazing A1 5 gt 10 Urban Commercial educational rooms used by groups of people Multiplier for calculating maintenance factor A1 10 gt x 1 Normal vertical glazing Exposure multiplier for calculating MF A1 11 gt x 1 Vertical glazing Normal exposure for location Maintenance factor gt 90 Total transmittance gt 0 62 void glass glazing mat 0 0 3 0 68 0 68 0 68 A 6 4 skies sky rad skyfunc glow skyglow 0 0 4 85 1 04 1 2 0 skyglow source sky 0 0 4 001 180 skyfunc glow groundglow 0 0 4 8 1 1 8 0 ol Axel Jacobs Radiance Tutorial
37. meters stored in the file views nice uf rvu vf views nice vf scene oct Figure 13 Our first interactive view Once the rvu window is up there are a number of interactive commands to adjust parameters and views You will probably have to adjust the exposure of the image before you can see all the details correctly The most commonly used commands are listed below They may be typed in full or called by the first letter e g e for exposure prior to Radiance version 3 6 rvu used to be called rview 17 Axel Jacobs Radiance Tutorial Command Explanation aim Zoom exposure Set the exposure frame Set frame for refinement last Restore the previous view new Redraw display pivot Pivot view about selected point quit Quit rotate Rotate the camera set Change program variable trace Trace a ray view Change view parameters write Write picture file Please look up the exact syntax and more detailed explanation in the rvu man page Another very hand little program is objview It calls rvu for an interactive preview of one or more objects The difference between the two is that rvu will only work on octrees i e compiled scenes whereas objview takes material mat and geometry files rad as inputs so the compilation is unnecessary Additionally objview will put light sources into the scene so objects can be looked at without putting a sky or luminaires into the scene objview ma
38. modified not just parts of it For what we ve done so far no material definitions were required This is going to change 2 2 3 More Complex Scenes The next exercise will produce something a bit more useful We are going to build a simple room with a window opening The room will then be used for our daylighting excercises 1 Create a room that is 4 0 m wide x dimension 5 0 m deep and 3 0 m high Give it the material wall_mat Call the genbox generator from the command line and direct the output of the command into a file objects room rad genbox wall_mat room 4 5 3 gt objects room rad 2 Change the material of the polygons that form the floor and the ceiling to floor_mat and ceiling mat respectively The materials wall mat floor mat and ceiling mat are already defined in materials course mat You ll find the listings of most files used in our exercises in Appendix A 6 of this document 3 Lower the south wall to create an opening setting the height of the wall to 1 0 m See Fig 11 for help 4 Create a pane of glass that fits into the new opening Make sure there are no gaps and that the entire room remains airtight Assign glazing_mat as a modifier 5 Create a file called furniture rad from which you call xform to place a table in the scene and a couple of chairs around it You ll find them in objects table rad 15 Axel Jacobs Radiance Tutorial 4 0 5 0 3 0 Figure 11 A simple room with an opening
39. modifier plastic identifier 0 0 5 red green blue specularity roughness plastic is a material with uncoloured highlights All values are in the range between 0 and 1 Specularity values above 0 1 and roughness of more than 0 2 are uncommon and look unrealistic The material metal is similar to plastic except that it produces highlights which are modified by the surface colour For metal the specularity is usually above 0 9 modifier glass identifier 0 0 3 rtn gtn btn glass is similar to dielectric but it is optimized for thin glass surfaces n 1 52 One transmitted ray and one reflected ray are produced The glass primitive requires us to specify the red green and blue transmissivity tn as arguments This is a somewhat inconvenient since manufacturers specifications as well as measurements are done for the transmittance Tn To convert from transmittance to transmissivity use the simple formula tn 1 09 x Tn The transmissivity is always higher than the transmittance For instance standard 88 transmittance glass has a transmissivity of 0 96 Note that this formula looks different to the one in the Radiance Reference Manual 8 It is much simpler but produces the same results You can find a discussion of the full vs this simplified formula in the Radiance Cookbook 2 A 1 2 Surfaces modifier sphere identifier 0 0 4 xcent ycent zcent radius 44 A APPENDICES modifier polygon identifier 0 0
40. nce image format directly To convert a Radiance image file to PNG format type convert gamma 2 2 images chair_rpict_pfilt hdr images chair_rpict_pfilt png The PNG image format utilses a loss less file compression which is perfect for reports and similar documents where the overall document size is not important If you want to publish the images on the Internet you want to make sure the file size is as small as possible in which case it is advisable to use the JPEG format instead JPEG images use a lossy compression which creates potentially much smaller files but might suffer from artifacts when high compression factors are used Compression factors below 50 will almost certainly exhibit such artifacts A compression factor of 100 which is the maximum will minimise such problems but results in larger file sizes convert gamma 2 2 quality 80 images chair_rpict_pfilt hdr images chair_rpict_pfilt jpg It is also possible to create GIF images however this format can only display a maxi mum of 255 colours The PNG format does not have those disadvantages The mogrify program of ImageMagick allows for the quick conversion of multiple images to a different format Combined with a little shell magic it is possible to convert a large number of files in one go cd images for file in hdr do normtiff file basename file hdr tif done mogrify gamma 2 2 format jpg tif cd to convert to TIFF using Radiance
41. nd patterns are optional The first primitive in this chain has no modifier so void is used The identifier of the first primitive becomes the modifier of the second one We need at least one material primitive and one geometry primitive void plastic chairmat chairmat cylinder legi 10 2 DESCRIBING A SCENE IN RADIANCE COB texture s patterns s material geometry object Figure 4 Describing an object It is possible however to have more than one material applied to an object In this case the primitives are hooked up like a chain connected by identifier modifier pairs void brightfunc dusty dusty texfunc woody woody plastic chairmat chairmat cylinder legl Patterns modify the reflectance of a material textures are perturbations of a surfaces normal Below is one example of each described by a mathematical model The material descriptions are listed in Appendix A 5 Texture gt Figure 5 Example of a Radiance texture Water Patton gt Figure 6 Example of a Radiance pattern Wood The second line in every primitive contains all string arguments that are needed to describe the primitive The very first character n is an indicator for the number of string arguments to follow The third line must always read 0 It was intended to be used for integer arguments when new primitives are introduced into Radiance but until now no p
42. nerators It creates outward pointing surfaces normals by default To swap this use the i switch with genbox Surface normal Figure 10 Direction of the surface normal The surface normal follows the right hand rule Form a loose fist with your right hand but have your thumb stick up Hold your hand in such a way that the axis defined by your thumb is perpendicular to the plane of the polygon Now turn your hand around the thumb axis following the direction given by the other four fingers If the indices follow the same direction the surface normal of the polygon is pointing into the direction of your thumb Otherwise it s the opposite Please see Fig 10 To get a rough idea about the dimensions and position of an object use the getbbox command It returns the minimum and maximum of an enclosing box along the x y and z axis getbbox chair rad xmin xmax ymin ymax zmin zmax 0 0 5 0 0 5 0 1 Use your favorite text editor to create the description of a sphere in a new file named objects things rad The general syntax is modifier sphere identifier 0 0 4 xcent ycent zcent radius Look at your first Radiance object with the objline command It creates what is known as a meta file which can not be viewed directly To display it on the screen simply pipe it into xiimeta objline objects things rad xiimeta Click anywhere on the picture to quit Also see what getbbox returns when called with objects things rad now N
43. option to rvu echo 0 0 0 00 1 rtrace I h ab 1 sky oct 5 591661e 01 5 591661e 01 5 591661e 01 Since sky oct contains the description of a non coloured grey sky all three colour chan nels have the same value of 5 587436e 01 or 55 87 W m This is an irradiance reading If the sky was non grey we d have to compute the average weighted irradiance To get the illuminance we simply multiply with the luminous efficacy of 179 lm W echo 7000 00 1 rtrace I ab 1 h sky oct rcalc e 1 179 265 1 670 2 065 3 10006 6961 The result is 10 000 lx This is no surprise to us because the sky was created with the b option to produce a horizontal illuminance of 10 000 Ix 5 2 2 Plotting luminance Values This exercise is based on the previous one and uses the bgraph command to plot a graph of lux levels at working plane height against the distance from the window The height of the working plane is usually taken to be 0 85 m Fig 29 illustrates the task at hand The readings are spaced 0 5 m with the first and last reading being no closer to the walls than 0 5 m Since the room is 5 0 m deep that s nine points in total The direction is up or z to get the horizontal illuminance A file called data line pts has Before Radiance version 4 1 Dec 2011 rtrace and rpict would issue a warning if the sky was without sun and if the number of ambient bounces ab was set to zero Such warnings can be disa
44. p www imagemagick org Axel Jacobs Radiance Cookbook 2012 URL http www jaloxa eu resources radiance documentation index shtml Axel Jacobs LEARNIX Web site Nov 2012 URL http www jaloxa eu mirrors learnix index shtml Axel Jacobs Radiance resources on www jaloxa eu URL http www jaloxa eu resources radiance Axel Jacobs UNIX for Radiance 2012 URL http www jaloxa eu resources radiance documentation index shtml Greg Ward Radiance man Pages 2008 URL http radsite lbl gov radiance whatis html Greg Ward Official Radiance web site 2012 URL http radsite 1bl gov radiance Greg Ward Radiance 4 1 Reference Manual 2011 URL http radsite 1bl gov radiance refer refman pdf Greg Ward Larson and Rob Shakespeare Rendering with Radiance The Art and Science of Lighting Visualisation Morgan Kaufmann Publishers San Francisco 1997 Radiance Community Radiance Online Web site Nov 2009 URL http www radiance online org Raphael Compagnon Radiance Course on Daylighting 1997 URL http radsite lbl gov radiance refer rc97tut pdf Thomas Bleicher su2rad Radiance Exporter for Google Sketchup 2008 URL http code google com p su2rad 43 Axel Jacobs Radiance Tutorial A Appendices A 1 The Main Primitives and Their Parameters A 1 1 Materials modifier light identifier 0 0 3 red green blue The RGB triplet for the light primitive is given as radiance values W m sr
45. package keep the files here data files that define grid points pts and any other data files that are not directly part of the scene docs any correspondence relating to the project as well as standards downloaded web pages etc images HDR images hdr I always keep the Radiance images and additionally create PNGs or JPEGs materials Radiance material files mat objects Radiance geometry files rad results Numerial results usually illuminance or daylight factor calculations with rtrace as well as any graphs created from them skies Radiance sky definitions both geometry and materials tmp any temporary files apart from ambient files amb All files in here may be deleted before a projects gets archived views any view file uf octrees Compiled Radiance octrees oct I tend to only keep RIF files rif in the top level directory of a project Everything else gets tucked away in some sub directory It is also a good idea to make generous 46 A APPENDICES use of README txt files In those you should write notes to yourself and anybody who might potentially be confronted with making sense of all the files explaining what the files are who created them and for what purpose how to use scripts you might have written etc A 4 Files Used in the Course File Name Use objects chair rad simple chair incl materials objects table rad simple table incl materials objects arrows rad a
46. r to get convincing images and more importantly realistic readings In com puting terms such an excercise is called a sensitivity study It is part of any building simulation done properly since it is the only way of determining reliable and accurate settings for the calculation engine 39 Axel Jacobs Radiance Tutorial Working Plane llluminance Effect of ad option 5000 ambient bounces 4000 ab 2 _ ab 6 Q 30001 O 3 ab 8 9 E 2000 a E 1000 0 1 2 3 4 5 Y Position meters Figure 30 An illuminance graph with low accuracy settings 40 6 THE JOY OF RENDERING 6 The Joy of Rendering 6 1 Too Much to Remember rpict defaults displays more than 40 options that allow complete control over all aspects of the rendering process While this allows experienced Radiance users to fine tune the results even they sometimes wish they could just hit a button and get some result quickly without having to fiddle all those options This is certainly even more true for the beginner We already found out that sticking to the defaults hardly ever produces the desired result 6 2 The rad command But don t despair help is there It comes in form of the rad command Once the control file is set up which doesn t take more than a couple of minutes a short command will either bring up an interactive view of the model with rvu or create a high quality image calling rpict But it does ev
47. re required from an image or if other values such as pixel position or the ray direction are of interest the ximage command can be of help The L key will display the luminance illuminance value at that point on the screen If ximage was started from a command line typing the T key or pressing the middle mouse button will print out one or more of the following Ray origin ray direction radiance value luminance value or pixel position This output can be controlled with the o option when calling ximage It can then be processed in a spread sheet or dealt with directly for instance with the rcalc command 10Until version 4 1 of Radiance Dec 2011 this had a default of nits which is the same as cd m2 It now defaults to cd m2 This and the cp option have been available in Radiance HEAD since Jan 2012 and will be released in Radiance proper with version 4 2 35 Axel Jacobs Radiance Tutorial luminance image Y Exposure Y Overlay adjustment of background N N pfilt J exposure adjusted luminance image Y Y falsecolor falsecolor cl falsecolor cl ip J 1 ca m2 ip J 1 cd m ip J 1 cd m2 false colour luminance image Figure 27 Flowchart for creating false colour images of the pixel luminance 5 2 Analysing Models with rtrace rtrace traces rays given to it on STDIN and produces the result on STDOUT Like the two other r commands rvu and rpict it operates on an octree
48. rimitive uses integer arguments The last line holds real arguments or floating point numbers Again the integer in front m indicates the total number of arguments to follow 11 Axel Jacobs Radiance Tutorial Comments are preceded by a hash sign and proceed to the end of the line If the first character in a line is an exclamation mark then this is taken as a shell command The line is executed and the result of this command returned 2 2 Describing the Geometry 2 2 1 Approaches to Modelling All Radiance scene files are stored as plain text This allows us to edit them with any text editor It is thus possible to build up a model by simply deciding which geometry primitives to use and supplying the required coordinates dimensions etc To aid in the creation of such hand build models Radiance comes with a number of helper programs that are commonly referred to as generators You can get a list of available generators by running the following command in your terminal ls usr bin gen genblinds genbox genclock genprism genrev gensky gensurf genworm In this tutorial we will be using the genbox command to create a simple rectangular room as well as gensky which defines the distribution of certain CIE defined standard skies The complexity of hand generated models is limited You will find that generating the scene geometry with a CAD or 3D modelling package is more convenient and faster
49. rrows indicating the coordinate system materials course mat material definitions skies sky rad definition of sky and ground skies sky_overcast mat material for an overcast sky views nice uf example view file room rif Radiance control file data line pts points for illuminance measurements luz plt plotfile for bgraph A 5 Material files for the pattern and texture example The board and the basin are both 1 by 1 unit in dimensions A 5 1 wood mat void brightfunc zwoodgrain 4 zgrain wood_pat cal s 005 0 11 zwoodgrain plastic board_mat 0 0 5 67 54 37 00 A 5 2 wood pat cal Wood grain pattern A1 magnitude 0 to 1 xgrain woodgrain Ring Py Pz along x axis ygrain woodgrain Ring Px Pz along y axis zgrain woodgrain Ring Px Py along z axis woodgrain r hermite 95 A1 20 95 A1 20 3 3 1 tri r 1 AT Axel Jacobs Radiance Tutorial Ring a b sqrt 25 sq mod a 50 25 sq mod b 50 25 A 5 3 v 6 0 3 3 fnoise3 Px 40 Py 40 Pz 100 water mat oid texfunc wavy xwrink ywrink zwrink wrinkle cal s 25 2d wavy dielectric wavy_water 0 0 5 v 0 0 5 A 5 4 9 9 91 1 330 oid plastic basin_mat 5 7 5 00 wrinkle cal A texture function for wrinkled materials 11 23 93 Greg Ward A1 average rise of wrinkles A2 average run of wrinkles A3 average spacing of wrinkles diri noise3 Px A2 3 Py
50. sampled Since the sky is made of glow it does not take part in the direct calculations resulting in the black interior 28 4 HOW RADIANCE WORKS To view the scene it is sufficient to set an ambient value that is greater than zero In Radiance ambient light is light that is not emitted from a source but instead is assumed to be constant over the whole scene Remember that in reality the intensity of the illuminance decreases with the squared distance from the light source To determine the value of the ambient irradiance the following formula can be applied The av option enables us to supply different values for the red green and blue channel however the three of them will usually be the same Eamb 1797 5 For outdoor simulations set av to the Ground ambient level as generated by gensky For indoor scenes the following approximation may be used Ramb 1 Start with an av setting that could be about right 2 Run rvu and interactively set the exposure of the image don t forget to set ab Typing e at the rvu prompt will return the current exposure 3 Re run rvu with an av of 0 5 exposure 4 Repeat 2 and 3 a few times until the values no longer change dramatically Set av to a value that is equivalent to 500 Ix and call rvu again rvu vf views nice vf w av 89 89 89 scene oct Different faces of the room can now be distinguished but the image looks very artificial because all obje
51. t command Run it without any options to automatically set a good exposure without having to worry about the correct exposure multiplier If the dynamic range of the image is too high the bright regions in the image will become washed out while subtle shades of dark grey turn into black It is possible to take the unfiltered image and compress the dynamic range so that both dark and bright regions are visible Radiance supplies the normtiff program for this which may also be used to mimic certain characteristics of the human visial system normtiff images chair_rpict hdr images chair_rpict_normt iff tif convert images chair_rpict_normtiff tif images chair_rpict_normt iff png a 1 0 Default of Im b 1 8 Used in printing c 2 2 Default for Ra d 3 0 For comparison ageMagick s convert diance s normtiff and ra_tiff Used for CRT monitors Figure 19 The same image with different gamma values applied The image was prepared with normtiff rather than pfilt and ra_tiff This ensures that there is pure black and pure white in the image The gamma value affects mostly the mid tones It is very important to be aware that Radiance s normtiff and ra_tiff default to a gamma correction of 2 2 while ImageMagick s convert has a default of 1 0 19 shows the same image with different gamma values applied 26 3 PREVIEWS VISUALISATION AND IMAGE CONVERSION ImageMagick is one of the few packages that can read the Radia
52. terials course mat objects chair rad 2 3 Describing the Materials 2 3 1 Standard Materials A total of 25 different materials are available to describe the characteristics of the surfaces They range from the simple to use plastic or metal to the more complex ones like dielectric and BRTDfunc which allow for the most accurate and difficult use but has settings for all directional aspects of reflectance and transmittance Please refer to 8 for a complete list as well as detailed descriptions Some further details can also be found in Appendix A 1 1 of this document The material used for the majority of cases is plastic which defines a surface that does not alter the colour of the highlights i e highlights appear in the colour of the light source rather than the colour of the material This is true for most materials around us be it wood paper concrete plastic or fabric Those are the arguments that the plastic primitive expects modifier plastic identifier 0 0 5 redrefl greenrefl bluerefl spec rough 18 2 DESCRIBING A SCENE IN RADIANCE All values must be within the range of 0 1 Most materials in reality have a rough ness below 0 2 and a specularity below 0 1 The contribution of the individual RGB components towards the average reflectance is weighted and equates to p 0 265R 0 670G 0 065B 1 for metal and to p 0 265R 0 670G 0 065B x 1 S S 2 for plastic with S being the specularity of
53. the material Don t get confused when reading through old documentation You might find differing multipliers there As of version 2 5 Radiance uses the multipliers found in Eqn 1 The reason for this has to do with cones in the retina of our eyes which are more responsive to green light than they are for red and blue Use your favorite image manipulation package such the The GIMP to pick a nice colour and apply it to the seat and back of our office chair The range of colours in most graphics packages is between 0 and 255 So you ll need to scale this down to a range between 0 and 1 What is the reflectance of the fabric Colour Picker Mozilla Firefox S www jaloxa eu resources radiance colour_picker index shtm Colour Picker for Radiance Red LL 0 300 Green A O 0 500 Blue Cs ous Hue Ee ae E Saturation SH 0 400 Value 0 500 Material e plastic metal Specularity WE TI 0 040 0 matte 0 07 satin Roughness W 0 000 0 polished 0 2 low gloss Reflectance DS Results Options Import Chooser ToDo Thanks Render Generate Radiance preview Render Normalised 0 680 1 133 0 940 Primitive Reflectance rho 0 464 void plastic identifier 0 o 5 0 3 0 5 0 415 0 040 Figure 14 The JALOXA colour picker is a handy tool for specifying materials There is quite a useful colour picker for Radiance on the JALOXA web site You may use it for picking a plastic or metal material
54. ubble polygon cone cup cylinder tube ring mesh instance Materials light illum glow spotlight mirror prism1 prism2 mist plastic metal trans plas tic2 metal2 trans2 dielectric interface glass plasfunc metfunc transfunc BRTDfunc plasdata metadata transdata antimatter Textures texfunc texdata Patterns colorfunc brightfunc colordata brightdata colorpict colortext brighttext Figure 3 Some of the Radiance primitives from left to right a polygon of type glass a sphere of type dielectric a cylinder of type plastic a cone of type metal a ring of type plastic with a brightfunc texture applied The syntax for any primitive follows this scheme modifier type identifier n S1 2 Sn 0 m R1 R2 Rm The type has to be one of the predefined surface material pattern or texture types that are known to Radiance The identifier can be freely chosen but should be unique within your project Please refer to Appendix A 1 for the most commonly used primitives and their parameters or to 8 for a full list of primitives and their parameters Before a surface primitive can be used a material primitive must exists whose identifier is the same as the modifier of the surface primitive By chaining several material and texture pattern descriptions together very detailed and realistic materials can be defined This chain is shown in Fig 4 While material and geometry primitives are always required textures a
55. ues in the image to colours This makes the interpretation easier for us humans since we are more adept to distinguish colours than shades of grey The following command line will do just this falsecolor ip imagegs scene hdr gt images fc_defaults hdr falsecolor creates a legend with the mapping of colours to photometric values The default label is cd m To make the displayed values a bit rounder set the number of divisions to ten and pick a round number for the maximum scale value the default here is auto falsecolor ip images scene hdr s 500 n 10 gt images fc_better hdr Fig 25 shows the results of these operations The image on the left was created with the default options the one on the right has some adjustments made to it a Default options b Better scale and nicer legend Figure 25 falsecolor called with the default options usually isn t what you want It is possible to use values from one image let s say an illuminance picture and overlay them onto another one such as the corresponding luminance picture This only makes sense when using contour lines rather a full false colour image The following command creates false colour contour lines of the luminance which are overlayed onto a background image as shown in Fig 26 on the left falsecolor ip images scene hdr cl s 500 n 10 gt images fc_overlay hdr To have contour lines of the illuminance instead use The default pa
56. ur window as if it was a real light source This is done with the mkillum command and is explained in the Radiance Cookbook 2 Raphael Compagnon s Radiance Course Notes 11 feature a table showing the minimum number of sample rays needed to certainly hit a glow source that sustains a certain solid angle Here are examples taken from there Angular Resolution Required ad Required ds 1 33863247 0 02 5 54446 0 09 10 3455 0 17 20 230 0 35 30 50 0 54 31 Axel Jacobs Radiance Tutorial It is clear that as the light source gets smaller the number of ambient sample rays required to hit the glow source explodes For very small sources this stochastic sampling becomes too unreliable and computing intensive 4 2 Ambient Parameters The following tables are copied from the file rpict options which is distrisbuted with Radiance Only ambient parameters are listed Please refer to the original file for a complete listing The column labelled Very Accur is not from the original table but was added because it gives you a better idea about appropriate options for accurate daylighting simulations 4 2 1 Useful Ranges Parameter Description Min Fast Accur Very Accur Max ab ambient bounces 0 0 2 5 8 aa ambient accuracy 0 5 0 2 0 15 0 08 0 ar ambient resolution 8 32 128 512 0 ad ambient divisions 0 32 512 2048 4096 as ambient super samples 0 32 256 512 1024 min for fastest crudest renderin
57. well the reading This is done with the o option The default is ov which prints the values Over writing this with oov will output the position too While we are fiddling with the command line options we also need to get rid of the header h cat data line pts rtrace I ab 3 h oov scene oct 2 00e 00 5 0e 01 1 85e 00 6 037e 00 7 387e 00 8 524e 00 2 00e 00 1 0e 00 1 85e 00 3 819e 00 4 673e 00 5 392e 00 2 00e 00 1 5e 00 1 85e 00 1 349e 00 1 651e 00 1 905e 00 To get the reading in lux rather than red green and blue irradiance values Eqn 3 has to help us out once more cat data line pts rtrace I ab 3 h oov scene oct rcalc e 1 2 2 179 265 4 670 5 065 6 gt results lux csv cat results lux csv 0 5 1271 4789 1 804 313407 1 5 284 135595 2 477 732247 2 5 463 546922 3 405 675942 3 5 387 179138 4 431 251321 4 5 158 74665 Prepared for you is a file named luz plt which gives some instructions to the bgraph command Modify it as you like To output to the screen and to a PostScript file resp use the following two command lines bgraph lux plt xiimeta bgraph lux plt psmeta gt results graph eps The plot in Fig 30 shows the results for 2 4 6 and 8 ambient bounces You will see that the graph changes dramatically for small numbers of ab but then approaches a final correct value Such and similar plots are a good approach to fine tune the parameters for rpict in orde
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