An Easy-to-Use Graph Drawing Package
Contents
1. The page size and packing area size only have to be given when they change and all subsequent plotting is laid out according to the latest details This usually means that layout is defined at the beginning of a pro gram and not referred to again If a packing area is defined which is too large for the page size it is re duced to fit in the page if the first graph of a page is too large for the packing area it is reduced to fit inthe packing area and all the graphs in the page are re duced by the same factor so that the required propor tions are maintained Plotting on graphs With an area of paper automatically claimed and say a pair of axes drawn within the area the programmer s own units used by SIMPLEPLOT to mark off the axes are then used to refer to the coordinates of points for plotting Coordinates may be expressed as Cartesian X Y or polar R Theta with Theta expressed in degrees or radians For a Smith chart the complex value to be plotted may be passed by the programmer to SIMPLEPLOT which will then convert this value to appropriate Cartesian coordinates for plotting The same plotting subroutines operate on linear or logarithmic axes polar graphs or Smith charts the interpretation of the coordinates is recognized within the subroutines by checking flags set up when each graph is started but may be redefined during the graph drawing process e g switching from polar in degrees to polar in radians2. Figure 2 Example layout of graphs using PACKIN February 1980 PLOTTER OPENED ROOM FOR GRAPH AT RIGHT HAND SIDE OF LAST GRAPH FIND AN AREA OF PAPER AND DRAW AN A4 PAGE DEFINE 16 CM X 21 CM PACKING AREA INSIDE PAGE DRAW GRAPH TO RIGHT OF LAST GRAPH WITH 2 CM GAP ROOM FOR GRAPH BELOW LAST ROW OF GRAPHS DRAW GRAPH AT TOP LEFT HAND CORNER OF PACKING AREA ORAW GRAPH AT LEFT HAND EDGE OF PACKING AREA BELOW LAST ROW OF GRAPHS WITH 2 CM GAP Labeling of graphs Anyone wishing to set a title or key on a graph by hand will tend to think of it in general terms relative to the graph as a whole and will want the lettering to be a reasonable rather than specific size The position of titles and keys is therefore given in descriptive rather than coordinate form referring to their general location Titles and keys may be placed vertically T top of graph B bottom of graph H higher than top L lower than bottom and horizontally L left C center R right Size of lettering The size of lettering for captions titles etc is automatically calculated being related to the overall size of the graph but adjusted where gt RE ES RSR Figure 3 Comparison of effect of different framework sizes on the size of the lettering etc 72 necessary to make the required text fit in th
3. PEN Change pen CHANGE Change color and line types for Smith chart LIM3D Change limits for SOLID SKETCH ENDPLT Close plotter Appendix 3 Interface between SIMPLEPLOT and alternative hardware systems SIMPLEPLOT is written in ANSI standard Fortran IV and has been implemented successfully on a number of dif ferent mainframes The interface between SIMPLEPLOT and graphics devices is through a set of subroutines which address a par ticular output device JBOPEN toopen a plotter JBPLOT to move the pen to point X Y with X Y in system units with or without draw ing JBTEXT to write text JBEND to close a plotter JBDISP output a message of 40 characters to the monitoring device e g line printer JBPEN to select a pen if more than one is available JBNEW to set up a new picture JBSYMB to draw a special symbol JBCHNG to alter width of paper to be used from default JBDATA to assign values to COMMON variables Default settings relating to a particular device are set up in a COMMON area and are accessed by the above interface subroutines They indicate e whether special symbols need to be coded by SIMPLEPLOT e whether text may be rotated e whether the character width is variable e the conversion factor from centimeters to system units e default paper size width and length whether either default paper length or width may be changed by program e whether a graph may be turned thro
4. The messages coming out of SIMPLEPLOT are enclosed in round brackets to distinguish them from other displays on the monitoring file MESSAGE PLOTTER OPENED BY SIMPLEPLOT PLOTTER CLOSED BY SIMPLEPLOT GRAPH COMPLETE GRAPH INCOMPLETE COMMENTS No errors detected Some out of range plotting omitted GRAPH OMITTED Plotter already closed by program GRAPH OMITTED TOO BIG GRAPH OMITTED CONSTANT DATA GRAPH OMITTED ZERO LENGTH GRAPH OMITTED ZERO COUNT Ee pian GRAPH OMITTED LOG AXIS THROUGH ZERO P SURFACE OMITTED CONSTANT DATA SURFACE OMITTED ZERO LENGTH SURFACE OMITTED ZERO COUNT CONTOUR GRAPH OMITTED CONSTANT DATA CONTOUR GRAPH OMITTED ZERO COUNT HISTOGRAM OMITTED ZERO COUNT parameters used in setting up of graph Errors in the number or types of parameters are not detectable from within the subroutines and therefore cause undefined failures Appendix 2 Subroutines offered in SIMPLEPLOT Subroutines for special graphs HISTGM Draw histogram SOLID Draw cross hatched hidden line surface i picture SKETCH Draw outline hidden line surface picture SLICED Draw a sketch with contours on it CONTR Draw contour graph Setting up subroutines NEWPLT Set up Cartesian graph with no drawing JBAXES Set up Cartesian graph and draw axes JBPOLE Set up polar graph and draw axis and circle SMITH Set up Smith chart Graph plotting subroutines JOINPT Join this point to last
5. 3 D plot etc is required an area of unused paper is automatically claimed At the simplest level an area of paper of given dimensions is found giving a 2 centimeter clearance from any other drawing previously done This is per formed entirely autonomously without the need for the programmer to specifically claim an extra area of paper or to keep an account of how much paper has already been used When a drum plotter is in use the package recognizes the roll width as a constraint on the plot ting area Consider the two areas of paper in Figure 1 The first graph is drawn in the bottom left hand cor ner of the paper and subsequent graphs are drawn above the previous drawing as long as there remains enough room on the paper When no further room can be found a new column of graphs is drawn clear of the widest graphs in the previous line A default 2 centimeter clearance is left below and to the left of each graph Parameters to the system in which SIMPLEPLOT is to be implemented include the default length and width of paper available These are set up when SIMPLEPLOT is implemented see Ap pendix 3 Parameters which can be defined by the programmer include e alternative width to be used where a two width plotting device is available at a particular in stallation the maximum length to be used when the pro grammer requires to claim more paper than the default length made available and e the margin between individu
6. same data after plotting and literal parameters are always acceptable for single variables in subroutine calls The package has been so designed that its use parallels manual graph drawing and graph plotting may be added to existing programs without fun damentally altering the program structures Structure of programs using SIMPLEPLOT There are several setting up subroutines which define the type of graph to be drawn next e g Cartesian graph with linear and or logarithmic axes polar graph Smith chart Each requires parameters relevant to the requirements of a graph of that type The first feasible call of a setting up routine causes tho opening of the plotter and subsequent ones cause a new unused area of paper to be found or a new pic ture to be started on a screen The basic framework of the graph which defines its scales is drawn by the setting up subroutine Within such a framework the subroutines for joining points by straight lines or curves or for marking points or for plotting functions may be invoked to plot the graph itself The same subroutines can be used on linear or logarithmic Cartesian scales or polar graphs the interpretation of the coordinates is determined by the type of graph being drawn It is possible to switch between degrees and radians and between polar Cartesian interpreta tion of coordinates Histograms contour graphs and hidden line surface drawings are each produced in their entirety from a
7. single subroutine call which will initiate both the setting up procedure to find a new area of paper and also the relevant plotting Additional labeling in the form of titles and keys can be added easily to a graph at any stage of its pro duction once it has been set up Service subroutines are included for enabling the request of more paper than a given default this must be invoked before the plotting device is opened and for producing graphs on pages of a chosen size and with specified gaps between them These have a continuing effect having been called once and they apply to all subsequent graphs until another call to change them The closing of the plotter has to be specifically requested by the user program since no way could be found to make this automatic using standard Fortran IV STATE OF THE ART WORKSTYLE STATE OF THE SUNSHINE LIFESTYLE ADD IT UP IT S YOUR FUTURE The state of the art at Harris Controls Division It s a half a century of redefining and forwarding the concept of supervisory control and data acquisition SCADA systems It s current expansion to large scale energy management systems and power control centers around the world For you it s unencumbered opportunity Opportunity to be recognized and rewarded in a rapidly progressing field Opportunity to design and produce in a professional environment that encourages contribution And yes Opportunity to live a bea
8. vals himself or he may leave it to SIMPLEPLOT to make a sensible choice Similarly the contour graph subroutine calculates a set of levels and draws a reasonable number of contour lines at equal intervals over the data range The same algorithm is used in these cases as for axis subdivision to determine the interval width What is required is to generate for any range of values a reasonable number of natural incre ments After extensive consultation with research workers we decided to provide between 7 and 13 in crements Within these limits the following algo rithm is used to select an interval 1 Scale the range of values up or down by an in teger power of 10 to convert it toa eD pe tween 2 and 20 i e range R 10 2 lt R lt 20 2 Choose an interval according to the value of R as follows R Interval Number of Intervals 2 0 3 2 0 25 8 13 8 2 6 4 0 5 7 13 6 4 12 8 1 0 7 13 12 8 20 0 2 0 7 10 3 Multiply the interval by 10 COMPUTER Labeling axes To ensure that the increment values on the axes are readable the following rules are ob served 1 All values on the increments are restricted to six characters at most 2 Whole number increments are drawn as inte gers without a decimal point 3 Figures which would exceed six characters are scaled and the power of 10 by which they are to be multiplied is added to the caption on the ax is e g 0 00000075 will be represented on
9. LL DASHED 1 2 0 1 0 0 0 CALL GRACUR X Y 1 2 11 C MOVE PEN TO SUITABLE PLACE TO WRITE TITLE CALL MOVT02 70 0 50 0 CALL CHAHOL 10HGINOGRAF C CLOSE PLOTTER CALL DEVEND STOP END C DRAW A PAIR OF AXES STARTING AT XLOC YLOC C WRITE A TITLE FROM CAP SUBROUTINE SETUP XLOC YLOC CAP DIMENSION CAP 1 C DEFINE POSITION OF GRAPH CALL AXIPOS 0 XLOC YLOC 120 0 2 CALL AXIPOS 0 XLOC YLOC 60 0 1 C DRAW HORIZ AXIS AND WRITE LABEL ON IT CALL AXIDRA 2 1 1 CALL MOVTO2 XLOC 40 0 YLOC 10 0 CALL CHAHOL 10HABSCISSA C DRAW VERT AXIS AND WRITE LABEL ON IT CALL AXIDRA 2 1 2 CALL MOVT02 XLOC 10 0 YLOC 20 0 C CHANGE ANGLE OF TEXT WRITING CALL CHAANG 90 0 CALL CHAHOL 10HORDINATE C RESTORE HORIZONTAL TEXT WRITING CALL CHAANG 0 0 C MOVE PEN TO SUITABLE PLACE AND WRITE TITLE CALL MOVTO2 XLOC 1 0 YLOC 50 0 CALL CHAHOL CAP RETURN END Figure 9 Fortran listing of GINOGRAF test program February 1980 4 Onthe bottom graph plot the two sets of points by joining them by two separate curves 5 For both graphs draw axes scaled to suit the data but including zero in both scales 6 Write captions on each axis of each graph a ti tle on each graph and a title for the page con taining the graphs The programs have been written assuming no knowledge of the data values so that the plotting is related directly to values which are read including the fixing of scales The data values used were t
10. O SCALE VERT AXIS C WRITE NCAP CHARACTERS FROM CAP AS A TITLE SUBROUTINE SETUP XFIRST XDELTA YFIRST YDELTA 1 CAP NCAP DIMENSION CAP 1 C DRAW AXES CALL AXIS 0 0 0 0 8HABSCISSA 8 12 0 0 0 XFIRST 1 XDELTA CALL AXIS 0 0 0 0 8HORDINATE 8 6 0 90 0 YFIRST 1 YDELTA C WRITE TITLE AT A SUITABLE PLACE ON THE GRAPH CALL SYMBOL 0 1 6 0 0 35 CAP 1 0 0 NCAP RETURN END Figure 8 Fortran listing of Calcomp test program COMPUTER DIMENSION X 11 11 2 READ 1 1 X 1 1 1 1 2 1 1 11 1 FORMAT F5 1 F6 3 F5 2 C SCAN DATA TO FIND RANGE OF VALUES C START WITH ZEROS SO THAT ZERO INCLUDED IN SCALES XMIN 0 0 XMAX 0 0 YMIN 0 0 YMAX 0 0 DO 10 1 4 11 1F X 1 LT XMIN XMIN X 1 IF X 1 GT XMAX XMAX X I DO 10 J 1 2 IF 1 J LT YMIN YMIN Y 1 J IF Y I J 6T YMAX YMAX Y I J 10 CONTINUE C START PLOTTING CALL CN925 C DEFINE PAGE SIZE CALL DEVPAP 210 0 290 0 0 C FIX CHARACTER SIZE CALL CHASIZ 3 0 3 0 C FIX SCALES OF AXES CALL AXISCA 1 8 XMIN XMAX 1 CALL AXISCA 1 8 YMIN YMAX 2 C CALL OWN SUBROUTINE TO DRAW AXES IN SUITABLE POSITION CALL SETUP 70 0 190 0 9HSYMBOLS C PLOT EACH SET OF DATA BY MARKING WITH SYMBOLS CALL GRASYM X Y 1 1 11 7 0 CALL GRASYM X Y 1 2 11 1 0 C CALL OWN SUBROUTINE TO DRAW AXES IN SUITABLE POSITION CALL SETUP 70 0 110 0 15HSMOOTH CURVES C PLOT EACH SET OF DATA BY JOINING WITH SMOOTH CURVES CALL GRACUR X Y 1 1 11 C SWITCH TO BROKEN LINES FOR SECOND DATA SET CA
11. With suitable software some graphics applications can be brought within reach of general computer users who have specific graphical requirements One such package is SIMPLEPLOT tae 50h i f f Special Feature An Easy to Use Graph Drawing Package Judy Butland and S D Butland University of Bradford Scientists and engineers whose interest in pro gramming is subsidiary to their main research ac tivities and who produce theories and results which can be represented graphically have wasted a great deal of time either plotting manually or developing often elaborate programs to draw graphs The plot ting software that has been made available has often been too clever offering so many flexible facilities that the non expert has difficulty in relating them to his own circumscribed requirements Or else it has not been clever enough often providing only a rudimentary set of graphical facilities that produce stylized and unprofessional looking output It was this environment that led to the design of SIMPLE PLOT Intended for research workers who are not primari ly computer programmers but who nevertheless want to produce high quality graphs for inclusion in reports theses and professional journals SIMPLE PLOT was designed in close collaboration with users to ensure that wherever possible the range of pictures produced relates closely to their actual requirements and that the instructions necessary to prod
12. al graphs The facility also exists to nominate the dimensions of pages on which graphs or sets of graphs are to be drawn In the simple case each graph is set within a separate page Where the dimensions of the graph are sufficiently smaller than the page size it is set within the page dividing the unused space in proportions 2 1 i e 2 left 1 right 2 bottom 1 top These proportions were chosen after consultation with a number of research workers and after deter mining the general practice in papers and theses Where the dimensions of a graph fail to fit within the page specified the graph is reduced to fit within the page with 3 centimeters to spare for a border retain ing the desired proportions In the case where more than one graph is required within a page the programmer has to work out the total area to be occupied by a set of graphs in one page and define this area the packing area be fore he draws them The packing area is filled from left to right from the top down The 2 centimeter gap between graphs must be included in the calculation of the area required Thus six graphs 6 centimeters by 5 centimeters may be packed in a page in two rows of three by defining a packing area COMPUTER width 3 6 2 24 centimeters height 2 5 2 14 centimeters or in three rows of two see Figure 2 by defining a packing area width 2 6 2 16 centimeters height 3 5 2 21 centimeters
13. cations in the plotting area are treated in different ways from each other but as the non progammer would expect e Positions of graphs are either automatically allocated or allocated in terms of the dimen sions of the areas they occupy e Labeling on graphs is positioned descrip tively e Plotting on graphs is described in units of the graph scales The programmer is never required to use any coordinate system except for the plotting on his graph 2 The provision of labeling facilities allows cap tions and keys to be written and related to ex isting plotting very easily and all lettering is written in sizes set by the package as appro priate to the function of the text and also the area available for the label Appendix 1 Monitoring of graphs error actions Whenever possible SIMPLEPLOT takes evasive action to avoid failure of plotting programs containing errors To assist interpretation of results messages are displayed on ne monitoring files to show whether or not errors have been Figure 12 Plotter output from GINOGRAF test program avoided and also to show at which stage the plotter is opened SEES cae 78 COMPUTER and closed One message is generated for every attempted graph one message is generated if the plotter is opened and one message is generated if the plotter is closed If a program terminates for any reason before the plotter is closed the message relating to the latest graph may be absent
14. e length available The basic character size S is calculated when setting up a graph sum of axis lengths 0 004 centimeters subject to a minimum of 0 14 centimeters This equa tion was arrived at after experiment taking into ac _ count the comments on alternatives by the research workers for whom the software was originally de signed If the character size of the output device be ing addressed is fixed then that size is used The basic character size S relates to the width of charac ter and the distance between lines of text is calculated on the assumption that no device draws characters of worse proportions than the line printer with proportions of height to width being 5 3 includ ing gaps between the lines and characters Individual character sizes etc are related to S as follows titles S 2 0 symbols S captions for keys S 1 2 broken line increments S 0 7 The effect of these proportions is to ensure that titles are drawn with larger characters than captions and that the size of symbols plotted and the gaps in brokerni lines relate to the overall size of the graph Ex amples of the effect of thus determining the relative sizes of lettering and broken line increments are given in Figure 3 Choice of intervals The histogram subroutine operates on raw data counting frequencies of values in a set of equal intervals before drawing the graph the programmer may either specify the width of inter
15. een checked for consistency Once the device has been opened a flag held in COMMON is set to indicate 69 that plotting has started The subroutine to open the plotting device is one of the small number of subroutines which form the device interface and which contain all the device dependent code Referencing positions on the plotting area Many currently available software packages require users to reference locations on the graphics device by un natural units SIMPLEPLOT provides three distinct graph drawing activities each with its own natural mode of referencing positions Position of graphs In some graphics systems the programmer is required to locate and draw for exam ple a pair of axes giving their position in centimeters relative to some origin on an area of paper This bears little relationship to the familiar task of finding an unused piece of graph paper where all that is re quired is to be presented with a clean sheet of paper of given dimensions Where the paper is on this or that part of the desk is of little significance as it is han dy SIMPLEPLOT therefore relieves the program Figure 1 Layout of five graphs each measuring 12 centimeters by 10 centimeters where the width of the available paper is a 30 cen timeters and b 80 centimeters 70 mer from having to know how his graphs are ar ranged on paper where this is the output medium Whenever a new pair of axes or new
16. eters by 6 centimeters one above the other 3 On the top graph plot the two sets of points by marking them by two distinct symbols C DIMENSION ARRAYS TO ALLOW EXTRA ELEMENTS FOR C FIRSTV amp DELTAV VALUES AND FOR ZERO TO INCLUDE C IN SCALE DIMENSION X 14 13 2 READ 1 1 X 1 1 1 1 1 2 1 11 1 FORMAT F5 1 F6 3 F5 2 C SET ZERO VALUES IN ARRAY ELEMENTS NOT CONTAINING C DATA X 1 0 0 12 1 0 0 13 1 0 0 C WORK OUT SCALES FOR BOTH AXES CALL SCALE X 1 12 0 12 1 CALL SCALE Y 1 1 6 0 24 1 C COPY SCALING PARAMETERS FOR Y TO END OF FIRST C DATA SET 12 1 12 2 13 1 13 2 C START PLOTTING CALL PLOTS 0 0 7 C MOVE ORIGIN TO SUITABLE POSITION FOR FIRST GRAPH CALL PLOT 7 0 19 0 3 C CALL OWN SUBROUTINE TO DRAW AXES CALL SETUP X 13 X 14 12 1 13 1 7HSYMBOLS 7 C PLOT EACH SET OF DATA BY MARKING WITH SYMBOLS CALL LINE X 2 1 1 11 1 1 1 CALL LINE X 2 1 2 11 1 1 2 C MOVE ORIGIN TO SUITABLE POSITION FOR SECOND GRAPH CALL PLOT 0 0 8 0 3 C CALL OWN SUBROUTINE TO DRAW AXES CALL SETUP X 13 X 14 12 1 13 1 SHLINES 5 C PLOT EACH SET OF DATA BY JOINING WITH STRAIGHT LINES CALL LINE X 2 1 1 11 1 0 0 CALL LINE X 2 1 2 11 1 0 0 C WRITE TITLE IN SUITABLE POSITION CALL SYMBOL 0 0 5 0 0 42 7HCALCOMP 0 0 7 C CLOSE PLOTTER CALL PLOT 0 0 0 0 999 STOP END C DRAW A PAIR OF AXES USING XFIRST XDELTA TO SCALE C HORIZ AXIS AND YFIRST YDELTA T
17. hese X Yl Y2 20 0 040 0 02 40 0 042 0 02 60 0 045 0 02 80 0 048 0 02 100 0 052 0 02 120 0 280 0 02 140 0 124 0 03 160 0 088 0 04 180 0 076 0 06 200 0 068 0 12 220 0 064 0 28 C DIMENSION ARRAYS TO ALLOW EXTRA ELEMENTS FOR ZEROS C TO INCLUDE IN SCALES DIMENSION X 12 Y 12 2 C SPECIFY PAGE SIZE AND SUITABLE LAYOUT CALL PAGE 21 0 29 7 CALL PACKIN 14 0 16 0 READ 1 1 X 1 Y 1 1 Y 1 2 1 1 11 1 FORMAT F5 1 F6 3 F5 2 C SET ZERO VALUES IN ARRAYS FOR INCLUSION IN SCALING X 12 0 0 Y 12 1 0 0 C DRAW AXES FOR FIRST GRAPH CALL JBAXES X 12 12 0 8HABSCISSA 8 Y 23 6 0 1 8HORDINATE 8 C WRITE TITLE AT TOP RIGHT CALL TITLE 1HT 1HR 7HSYMBOLS 7 C PLOT EACH SET BY MARKING WITH SYMBOLS DO 10 J 1 2 DO 10 1 1 11 10 CALL MARKPT X 1 Y 1 J J C DRAW KEY TO SYMBOLS AT TOP LEFT CALL SET KY 1HT 1HL 2 15 CALL MARK KY 1 14HFIRST DATA SET 14 CALL MARK KY 2 15HSECOND DATA SET 15 C DRAW AXES FOR SECOND GRAPH CALL JBAXES X 12 12 0 8HABSCISSA 8 Y 23 6 0 1 8HORDINATE 8 C WRITE TITLE AT TOP RIGHT CALL TITLE 1HT 1HR 13HSMOOTH CURVES 13 C PLOT EACH SET OF DATA BY JOINING WITH SMOOTH CURVES CALL BRKN CV X Y 1 1 11 0 CALL BRKN CV X Y 1 2 11 1 C DRAW KEY TO LINES AT TOP LEFT CALL SET KY 1HT 1HL 2 15 CALL LINE KY 0 14HFIRST DATA SET 14 CALL LINE KY 1 15HSECOND DATA SET 15 C WRITE PAGE TITLE IN CENTER LOWER THAN GRAPHS CALL TITLE 1HL 1HC 10HSIMPLEPLOT 10 C CLOSE PLOTTER CALL ENDPLT STOP END Figure 10 Fortran li
18. les define system constants such as default and maximum paper sizes and conversion factor between system units of mea surement and centimeters Each small subroutine performs one simple task such as move pen write text open plotter close plotter when facilities are available on the system subroutines may be in cluded to change pen or change paper width SIMPLEPLOT contains coding for drawing sym bols but if system hardware symbols are preferred a draw symbol subroutine may be supplied Suc cessful implementations have already been carried out on a wide range of mainframes from PDP 11 to CDC 7600 driving a variety of devices including drum plotters flat bed plotters and display devices SIMPLEPLOT is designed as a special purpose graphics package for drawing graphs and does not at tempt to serve as a general purpose plotting package Within the applications covered by SIMPLEPLOT generality has deliberately been sacrificed for ease of use whenever we thought these were in conflict Graphics standards therefore simplify the interfac ing of SIMPLEPLOT to different systems while in no way altering the user interface It has already been interfaced to widely differing graphical devices and systems through their own basic plotting software including PLOT10 Calcomp GINO F GHOST SPECTRE and many low level graphics systems We expect any form of standard which might be adopted
19. n to the function being drawn See Figures 5 7 Error actions All recognizable errors are evaded and suitable messages are directed to the line printer After each graph is finished a report is sent to the line printer in dicating whether or not any attempt was made to draw outside the area requested Attempts to plot outside the limits of the current graph are always ig nored An attempt to draw a smooth curve through two points gives a straight line though fewer than two are ignored unrealizable scales such as logarithmic scales through zero or a scale with equal minimum and maximum values are omitted and then all plotting calls are ignored until the next one which sets up anew graph It has been assumed that a set of incomplete graphs is very useful in debugging a plotting program and there are therefore no condi tions in which identifiable errors in attempting to plot cause the program to halt A full set of error messages and their significance are given in Appen dz Preserving data No parameter values are altered within the subroutines There is a single exception to this rule when one is plotting values on a Smith chart a com plex value is supplied to SIMPLEPLOT which cal culates the Cartesian coordinates on the plot corre COMPUTER sponding to this complex value These coordinates are then returned to the user program as parameters The programmer using them may therefore perform further calculations on the
20. r in 1967 She re ceived an M Phil at University of Bradford in 1979 for her work on SIMPLEPLOT David Butland is the head of User Ser vices in the Computing Laboratory at the University of Bradford England He is primarily concerned with the pro vision of central computing facilities re quired by research projects at the Uni versity His own research interests center around the generation of test se quences for large digital networks Butland received a BA in philosophy at the University of Manchester in 1964 and a PhD at the University of Bradford in 1978 for his work on the genera tion of diagnostic tests He is a member of the British Com puter Society and is married to Judy Butland COMPUTER
21. sting of SIMPLEPLOT test program 77 Comparison of test programs Comments have been included throughout the test program listings Figures 8 10 so that those unfamiliar with the par ticular packages should have no difficulty in under standing each line Apart from the obvious dif ferences in methods required for programming the different parts of the example it should be noted how often the word suitable occurs in the comments in the Calcomp and GINOGRAF programs Every time the comment refers to a suitable position the pro gram contains numerical values which have had to be calculated in advance by the programmer usually by drawing a sketch of the required layout The single use of the word suitable in the SIMPLEPLOT comments relates to the preliminary layout state ment everything afterwards is positioned in an ap propriate place by the package including keys which are not available as such in the other packages Because SIMPLEPLOT is designed specifically for graph drawing rather than general plotting some of the flexibility offered by other graphics packages has been strategically taken away from the user on _ the assumption that this flexibility complicates the _ plotting of graphs The major gain over other Pr gt packages is believed to be achieved in two general eS FE REN ee RES areas Figure 11 Plotter output from Calcomp test program 1 Three types of lo
22. the axis as 0 75 and the scale 10 will be added to the caption The effect of writing different ranges of values on axes of the same length is given in Figure 4 Provision of defaults Wherever choices are offered to the programmer defaults are offered when possi ble so that the learner can master a few rudimentary facilities initially and add enhancements toa working program later SMALL VALUE RANGE 10 3 Efficiency In addition to the obvious atbempte to produce 2000 o 2000 4000 compact and efficient code extra constraints have LARGE VALUE RANGE lt 10 been self imposed throughout the development of TARGE VALUE R l SIMPLEPLOT Figure 4 Effect of different ranges on axis lettering Video O A TV to Computer Input Device O A Computer to Film Output Device O Computer Controllable Sampling Patterns and Rates O 480 x 512 Element Resolution 8 Bit Gray Scale Model 270A lets your computer look at the whole world economically Four page data sheet includes specs block diagram flow chart Model 270A 4000 w Colorado Video Inc P O Box 928 Boulder CO 80306 303 444 3972 TWX 910 940 3248 COLO VIDEO BDR Video Instruments for Data Acquisition Processing Transmission Display Reader Service Number 10 Core store minimization None of the subroutines requires the specification of any working arrays of variable length Considerable effort has been ex Figure 5 Full solid fig
23. to represent a suitable vehicle for SIMPLE PLOT Comparison of SIMPLEPLOT with other packages SIMPLEPLOT was originally developed to satisfy local requirements when the alternative software available at the university was that supplied by Calcomp with their plotters Every facility offered was developed with ease of use as the prime con sideration and all routine tasks which are performed by the majority of graph drawing programs were ab sorbed into the package to relieve the user of the burden of organization It appears that SIMPLE PLOT has taken the concept of user orientation fur ther than other packages for drawing graphs partic ularly in the organization of layout and label position ing The effect of this on the task of writing a program to plot graphs is best illustrated by comparing the programming of a simple graph drawing problem us ing SIMPLEPLOT and other packages A test example For illustration a simple plotting example has been chosen which requires a set of com monly needed features together from one program Programs have been written to use the Calcomp soft ware GINOGRAF a graph drawing extension tothe GINO F package and SIMPLEPLOT to make full use of the facilities offered in each case to draw the specified graphs from simple programs see Figures 8 13 The chosen example is as follows 1 Read one set of 11 abscissae and two sets of 11 corresponding ordinates 2 Draw two separate graphs 12 centim
24. uce their pictures relate to the manual production of graphs with which they are all familiar Here are some of its facilities Framework definitions e linear and or logarithmic axes e Smith charts e polar axes Plotting within frameworks e straight lines from point to point e smooth curves through sets of points e curves of functions from function definitions e circles February 1980 0018 9162 80 0200 0069 00 75 1980 IEEE e different types of broken lines to distinguish curves e different types of symbols to mark points Plotting complete composite graphs e histograms e contour graphs e hidden line surface drawings Layout etc e keys e titles e layout in pages e organization within pages Four general rules have been consistently observed throughout the development of the subroutines 1 Do not require the programmer to make deci sions which can be made equally well or better by the package 2 Minimize use of core store mill time and plot ter time 3 Evade errors but give intelligible diagnostic information when errors are detected 4 Leave all parameters unchanged Decision removal Opening the plotter The plotter opening or device allocation is performed automatically as soon as the first feasible graph is attempted This involves defer ring the call of the subroutine to open the plotting device until all checks on parameters to the first subroutine purporting to draw a graph have b
25. ugh 90 on the output device e maximum size of an individual graph and e whether the size of an individual graph is fixed Setting up the above subroutines has proved to be a trivial task for all new output devices on which SIMPLE PLOT has been made available so far as new devices become available we expect the provision of the additional interface to be correspondingly simple W References 1 J Butland Surface Drawing Made Simple Computer Aided Design Vol 11 No 1 Jan 1979 pp 19 22 2 Calcomp Reference Manual Calcomp Fullerton Calif 1969 3 GINOGRAF User Manual CAD Centre Cambridge UK 1976 4 SIMPLEPLOT User s Handbook University of Brad ford UK 1978 Judy Butland has been computer of ficer for the Postgraduate School of Electrical and Electronic Engineering at the University of Bradford since 1970 She writes programs assists research students in programming and collaborates in the solution of computa tional problems associated with a wide variety of research proj ects in electrical ta engineering It is in this environment that ies research interests in providing simple graphic facilities for engineers have developed She studied mathematics at the University of Man chester Institute of Science and Technology from 1960 to 1963 but was first introduced to computing when working as a mathematical assistant for Manchester Business School in the University of Mancheste
26. ure Figure 6 Outline figure of Figure 5 Figure 7 Outline figure with contour markings 74 pended in developing methods for such tasks as drawing smooth curves through sets of points draw ing contour graphs and drawing hidden line surfaces which do not require any working arrays and yet pro duce good quality graphs Two extra bonuses derive from this principle 1 All parameters the programmer is required to specify are of direct relevance to him 2 The software is uniquely applicable to im plementation on computing systems with restricted core Plotting time minimization When composite tasks such as drawing axes or 3 D pictures are specified completely in a single subroutine call the pen movements are arranged to define an efficient travel ing distance to achieve the composite drawing The hidden line surface picture subroutines use different colors where they are available on an installation in order to distinguish the upper and lower sides of the surface and all the plotting of one color is completed before the other color is used so that the drawing is not slowed down by repeated pen changes A completely new set of subroutines have been made available to draw the outline alone of a hidden line surface using the same data and parameters as the subroutine to draw the full cross hatched picture This offers the advanatges of efficiency in both mill and plotter time and it gives a good approximatio
27. utiful affordable lifestyle on Florida s February 1980 scenic Atlantic shoreline Add it all up It s your future SOFTWARE DESIGN SENIOR SOFTWARE DESIGN ENGINEERS Design development and integration background Five plus years experience in Operating Systems Development Device Handlers Distributed Processing Computer to Computer Communication Telecommunication Diagnostic Development and or Large Scale Integration and Test Task leadership positions encompass design and project responsibilities and technical supervision POWER SYSTEM ANALYSTS ENGINEERS Experience in development of control and planning solutions for real time systems associated with computers in power industry problems Familiarity with current analytical techniques for the solution of load flow contingency conditions load forecasting and state estimation EE majors with graduate degrees and AGC EDC background Send resume with salary history to R B Storch Harris Corporation Controls Division P O Box 430IEC Melbourne Florida 32901 HARRIS COMMUNICATION AND INFORMATION PROCESSING An Equal Opportunity Employer M F 75 76 Implementation of SIMPLEPLOT on different configurations The subroutines have been designed to be transfer rable easily to different devices The transfer in volves setting about twelve common variables and writing a few small subroutines to SIMPLEPLOT specifications The common variab
28. with straight line BREAK Lift pen between two successions of JOINPT MARKPT Mark point with a selected symbol DRAWLN Draw line between point and zero XRANGE Marka range of X values YRANGE Mark a range of Y values DRAWCV Draw a smooth curve through a set of February 1980 Figure 13 Plotter output from SIMPLEPLOT test program BRKNCV DRAWFN BRKNFN FNRNGE DRAWCL BRKNCL JBCODE CARTES DEGS RADS points Draw a smooth broken curve through a set of points Draw a smooth curve from a function definition Draw a smooth broken curve from a function definition Change range for DRAWFN BRKNFN from default Draw a circle Draw a broken circle Calculate Smith chart coordinates from complex value Switch coordinate interpretation to Cartesian Switch coordinate interpretation to polar in degrees Switch coordinate interpretation to polar in radians Graph labeling subroutines DRAW AX TITLE SET KY LINE KY MARK KY BOTH KY BLNK KY Draw a single axis Write a title on graph Initialize a key Write a key for a broken line Write a key for a symbol Write a key for a line and symbol together Include extra space between key entries 79 80 Organizational subroutines SIZE Change paper allocation from default MAGNIF Set a scaling factor for all subsequent graphs PAGE Define a page size for all subsequent graphs MARGIN Change margin between graphs
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