Car Navigation System
Contents
1. 3 most critical performance scenarios 1 User wants to have the actual position and map with all the requested information available 22 25 Car Navigation System Radim Cebi amp and Pavel ernohorsk while navigating and be able to control the device with low response time We want to provide the screen refresh rate at 20 Hz and the same thread handles the input in that rate Our load estimates show that this should be possible even when all the other possible tasks are running in the same time User wants to re compute the route in short time while keeping the screen updated We will provide the route at 3 sec and will be refreshing the screen at 15 Hz while computing the route We estimate that this is possible but the CPU will be in the highest possible load User want to be informed by voice about the upcoming changes of direction etc as soon as possible Our voice module will check the change status every second which should be enough in even the route densest areas The requested computing load is low enough to be able to keep this frequency of checking the conditions Top 5 technical risks l Bad selection of route planning algorithm Overall usability of the device is influenced a lot by it s ability to give a driver really the shortest route that meets the given constraints If wrong algorithm slow not holding given constraints or unsuitable in some other way is chosen whole device may become completely unus2. e Customized operating system will be used for the device no controls and detection of HW on boot Supports requirement 10 Rationale it is not necessary to test or detect the HW because the HW configuration will be fixed and this way we can provide better start up times e High sensitivity GPS receiver will be used For example SiRFstar III Supports requirement 11 Rationale our device should be as accurate as possible e Rendering the screen will be handled by main thread which will have high priority Supports requirement 12 Rationale it is important that the screen refresh will not be dependent on other functions e Screen refresh rate 1s lowered to 15 Hz while computing new route Rationale We believe that it is useless to have so much computing power to be able to refresh the screen as fast as 5 25 Car Navigation System Radim Cebi amp and Pavel ernohorsk in navigating 20 Hz when the computation of the route is done only few times per hour We believe that this is better way than investing more money for HW performance which will be so rarely used and the 15 Hz refresh rate is still good enough We suppose that this is very good trade off e Maps and POIs will be updated via USB mass storage standard Statistics will be downloaded to PC via USB mass storage standard Supports requirement 13 14 Rationale this way we can achieve even better interoperability than stated in requirements and also it is more standardized solu
3. Performance tactics We are introducing concurrency so the most resources intensive tasks will have independent threads with appropriate priorities this tactics also gives us graceful degradation property for example if one of the not so important thread encounters some problem remaining sub system will continue working properly There will be main thread which handles screen updates user input and some components which do not need to run independently Other threads will be statistics update position update voice update RDS TMC update route computational thread The threads are given processor time according to their priority We are using only frequencies of updates which are as low as possible for usability We also bound the execution time for finding the best route to 3 sec Also the frequency of the user s input is bounded to 20 Hz as the GUI is running at that speed Thread diagram Car Navigation System Process Main Thread n esil uem fice al I Map Visualization Module Statistics Controller Module Map Module POI Module nu xr jt ru f Voice Update Thread Statistics Update Thread Route Computational Thread RES 4d Voice Module Statistics Data Module Route Module pz Ei Position Update Thread RDS TMC Thread L1 1 num Position Module GPS Controller Traffic Data Module RDS TMC Controller gt C C ER This diagram describes in which thread which component is running
4. and info panel I I l RenderMap zoom viewType l 1 GetActualPosition Visualize RenderlconsAndValues This use case is executed by periodically by a thread when the user is in map view It updates the screen It finishes when the screen is refreshed but then is executed almost immediately again 19 25 Car Navigation System Radim Cebis and Pavel ernohorsk UML Deployment Diagram LAS LE LEE af RDS TMC GPS satelite transmitter CNS Portable Device L Car Navigation System d This diagram describes which other devices are used with the device Only the CNS portable device is under control of developers and architects 20 25 Car Navigation System Radim Cebi amp and Pavel ernohorsk Performance analysis Frequencies of events and accuracy GPS s maximal accuracy for civilian use is about 3 m and minimal accuracy is about 15 m when at least 3 satellites are in the view The GPS HW can give a position and velocity direction time data every second for example the SiRFstar III GPS chip Position controller will update the actual position in frequency of 28 Hz provided that the maximal speed 300 kmph of the device and maximal GPS accuracy is 3 meters it will take 10e 5 hours to drive 3 m at this speed and that is 0 036 sec which gives us frequency of approx 28 Hz But it can ask for the data the GPS HW only once per second so the position be
5. be used Supports requirement 4 Rationale it is important to give the user fast suggest functionality while he is writing the address e Inevery screen there will be button to get back to main screen with the map and from the main screen it is possible to enter address in 3 clicks not counting clicks used for input first click on button to enter the destination second click to choose the type of the input of destination 1 e address coordinates third click to confirm the input 1 e address Supports requirement 5 Rationale user must be able to drive a car thus cannot be overwhelmed by controlling the device He must have fast access to most often used functions e Screen buttons must be at least 1 cm x 1 cm big for the common finger to fit there Supports requirement 7 Rationale most of the population have fingers thin enough to be able to control the device with them e Device plays the press sound after each touch confirming the successful input Supports requirement 8 Rationale user must be able to switch his focus on the route as soon as possible after the touch so he cannot check the screen if the order was taken into account Or sometimes he cannot pay attention to the screen and is pressing the buttons just by memory e High capacity batteries and the processor with low power consumption will be used Supports requirement 9 Rationale it must be possible to use the device without the charger for shorter journeys
6. Car Navigation System Radim Cebi8 and Pavel ernohorsk Car Navigation System Assignment for Software Architecting course at Technische Universiteit Eindhoven Radim Cebi and Pavel Cernohorsky 1 25 Car Navigation System Radim Cebis and Pavel ernohorsk Requirements Extra functional Performance 1 It re computes route to the desired destination in 3 sec 2 When information about some traffic problems is received through RDS it will be checked within 3 seconds whether this new information is relevant for current route and when yes re computation will be initialized 3 It recomputes route in case of diversion from computed route in 3 seconds after diversion is bigger than minimal accuracy see legend 4 While entering destination by address device suggests streets etc which starts with the entered letters within at most 0 3 seconds Usability 5 User can always set the new destination in at most 4 touches from any system state not counting touches used for writing 6 At least 80 of the screen is used for showing a map while system navigates user to some destination 7 Device is controllable by finger touches of 80 of population 8 User will be informed about successful screen touch Availability 9 While operating using batteries it will be able to be fully operational for at least 4 hours in the worst case no matter what functions user uses 10 After turned on device has to be operational except for
7. User can save any position into the one of 20 save positions slots 28 User can create at most 10 profiles which will be used for saving trip statistics information distance average speed exact time of the trip Trip in this context is one travelling on the given destination address 29 Device will be capable to store statistics of last 10 trips for each user profile 30 Statistics are saved in human readable text format 3 25 Car Navigation System Radim Cebi amp and Pavel ernohorsk 31 When the device is not connected to the electricity source it shows battery status in the main view map view 32 It informs the user about GPS signal strength and possible inaccuracy If there is no signal it shows special indication on the same place 33 There will be enough place to upload the maps of whole Europe in highest currently available accuracy Legend minimal accuracy 15 m maximal accuracy 3 m POI Point of interest 4 25 Car Navigation System Radim Cebi amp and Pavel ernohorsk Design decisions e Path finding algorithm with adaptive accuracy will be used It will iteratively refine the route maximally until the given time limit is exceeded in our case 3sec Supports requirement 1 3 Rationale this algorithm will return at least some result which will be very close to optimal one e Forsaving the addresses the data structure with lexically ordered items and thus fast access for suggest functionality will
8. able although everything else is working according to the specification Wrong handled concurrency of threads Working with threads always brings new risks to the system and handling them in the wrong way may introduce various performance problems that may cause violation of some of the requirements or in worse case wrong handling of the concurrent access to the data may lead to the severe data corruption Bad HW selection Big care needs to be taken also while selecting the proper hardware There has to be proper balance between the speed and the power consumption of the HW Using too fast HW may lead to big energy consumption and to violating some availability requirements On the other hand HW with the low power consumption might not be strong enough and some performance requirements may be violated Slow implementation of map rendering Wrong map rendering mechanisms may lead to big slow down of the main thread and to violating of some requirements For example GUI response time may be higher than required etc Bad underlying OS selection Choice of the right underlying OS affects not only the cost of the system but also influences simplicity of implementing desired functionality programming and debugging OS also has to have a good and if possible highly customisable or controllable thread scheduling algorithms 23 25 Car Navigation System Evaluation overview tables Radim Cebi8 and Pavel ernohorsk VALUE How much value does t
9. ating so that user will not have look for it on the map 19 Voice tells the user about the change of direction right after every change 1 min before the change when there is enough time for it and then at least 5 seconds before the change according to current speed 20 Voice instruction contains distance to the next action type of action after 100 meters turn left turn left stay 1n the left lane use second exit at the roundabout slow down and similar with different distances and directions 21 While showing the map there is a button to replay last voice instruction 22 User has possibility to switch the system into the night mode when it s luminance will be low enough not higher than luminance of recent car s control panel with speed meters not to disturb the user from driving when the system is placed in the car on the place described in the user s manual 23 User can select which info time distance from the target time to target distance to the next direction change next direction change types of POIs to show on the map velocity should be presented all the time together with the map 24 User can turn on off the speed warning by beep sound the fastest way which warns of speeding according to limits saved in map 25 After switching on the last planned route is displayed so the user can plan the route in advance 26 User can enter the destination by address coordinates touch or selecting from saved positions 27
10. eless without this function X Necessary for the previous function to work X It is necessary to give the user the information This is not needed for navigating This is not needed for navigating EFFORT how much effort will be needed for implementing this use case name of reviewer name of application Radim Cebis and Pavel Cernohorsky Car Navigation System implementation effort required O very little 7 very much Name of Use Case 0 1 2 3 4 5 6 7 Set destination by address X Set destination by coordinates x Compute route x Update position and time X Show map and info panel x Save position x Update maps x brief motivation This only needs some structures for address lookup It is just an input This just needs a small part of GUI Points will be internally saved in coordinates so nothing else special is needed It will be hard to choose and develop fast algorithm with best results which must take into account traffic information This requires the developer to learn GPS HW interface and to implement some error correction Good implementation is essential for good performance Easy to do just save the data to the persistent memory Easy to do just load new data VALUE How much value does this component contribute to the user of the system name of reviewer name of application Radim Cebis and Pavel Cernohorsky Car Navigation System phase 1 criticality to system operation O not valueab
11. face for voice and GUI module to ask for them e watches over the speed warnings Map visualization module e makes visualization of the vector map puts desired POIs on the map puts traffic information on the map puts route on the map handles types of view and view port zoom 3D top view translates screen position to position on the map for user input Statistics controller e switches statistics profiles provides reset of the statistics provides higher level interface for statistics data provides export of the statistics via USB is responsible for updating statistics data Voice module e provides audio output e gives orders to users according to route 11 25 Car Navigation System Radim Cebi8 and Pavel ernohorsk e offers volume change mute e plays click and beep sounds GUI e provides user interface e handles day night mode e propagates events to responsible modules e remembers which fields to show on the information panel 12 25 Car Navigation System Radim ebi and Pavel ernohorsk UML Sequence Diagrams Only the representative ones are presented Set Destination User GUI Voice module SetDestinationClick PlayClickSound A l Now the menu wich offers types of input to select the destination appears This use case is executed when the user clicks on the icon Set destination to set a new destination in map view It just shows the menu from which the u
12. his use case contribute to the user of the system name of reviewer name of application Radim Cebis and Pavel Cernohorsky Car Navigation System criticality to system operation O not valueable 7 extremely valuable Name of Use Case 0 1 2 3 4 5 6 7 Set destination by address X Set destination by coordinates X Compute route X Update position and time X Show map and info panel X Save position x Update maps X brief motivation This is the function is important for all the users This is useful just for small group of users This is the function which is why the system could be sold Necessary for navigating Necessary for navigating Increases usability of the system but it is not so important for its main function Increases modifiability of the system but when good maps are provided out of the box it is not so needed but the routes change in time CRITICALITY how critical is this use case to the overall operation of the system name of reviewer name of application Radim Cebis and Pavel Cemohorsky Car Navigation System criticality to system operation O not important 7 essential Name of Use Case 0 1 2 3 4 5 6 Set destination by address X Set destination by coordinates X Compute route Update position and time Show map and info panel Save position x Update maps X brief motivation 7 It is important to be able to give input It is important to be able to give input X System would be us
13. l I ComputingRoute l m i d T 4 4 4 ComputingRoute is calling GetAdjecentData as needed most probably a lot of times until it finds best result or all the given processing time was spent SaveRoute This use case begins when the SetDestination is invoked It finishes when the new route is computed and saved Update position and time a a A GetGPSLocation CorrectPosition SavePosition This use case is executed by periodical thread which updates position and time when the SetDestination is invoked It finishes when the new corrected position is saved 17 25 Car Navigation System Radim ebi and Pavel ernohorsk Select types of POI to show I I MenuClick I PlayClickSound ShowPOIClick PlayClickSound GetPOITypes poiTypes Now the GUI is showing screen with checkboxes and user can select unselect them OKButtonClick The checking unchecking of the boxes is processed by GUI which then calls Voice module to play sounds and is not shown in the picture SetPOITypes selectedTypes SetPOITypes selectedTypes This use case is executed when user wants to select which types of POI to show It finishes when user click OK and is back in map view 18 25 Car Navigation System Radim Cebi8 and Pavel ernohorsk Show map
14. le 7 extremely valuable Name of Component 0 1 2 3 4 5 6 7 GPS controller X Position module X Route module X Map visualization module X GUI X Map module X Voice module x brief motivation This component is necessary for system operations This component is necessary for system operations This component is necessary for system operations Necessary module but can be sufficient even when is not perfect Necessary module but can be sufficient even when is not perfect This component is necessary for system operations Valuable for user but can live with only graphic representation 24 25 Car Navigation System Radim Cebi8 and Pavel ernohorsk CRITICALITY how critical is this component to the overall operation of the system name of reviewer name of application Radim Cebis and Pavel Cemohorsky Car Navigation System phase 1 criticality to system operation O not important 7 essential Name of Component 0 1 2 3 4 5 6 7 GPS controller X Position module x Route module x Map visualization module X GUI X Map module X Voice module X brief motivation This component is necessary for system operations This component is necessary for system operations This component is necessary for system operations This component is necessary for system operations his component is necessary for system operations but might be slower or not so pretty looking This component is necessary for s
15. nd WaitForCoordslInput ContinueTouch I I I i I I 1 PlayClickSound i i I 3 SetDestingtion coords This use case begins when the user clicks in the input type menu that he wants to enter the destination by entering the coordinates It finishes when the destination was passed to the route module and the screen is back in map view 14 25 Car Navigation System Radim Cebis and Pavel ernohorsk Set Destination By Saved Position User GUI Voice module Route module l l SetDestinationBySavedAddress I I PlayClickSound I l GetSavddPositions pobitions E nti eh co a i i e aa a a WaitForPositionSelect j PositionSelect This use case begins when the user clicks in the input type menu that he wants to enter the destination by selecting from previously saved positions It includes the offering of list with saved positions It finishes when the destination was passed to the route module and the screen is back in map view Set Way Points SetDestinationClick SetWayPointsClick PlayClickSound PlayClickSound P ntil Cancel pressed PlayClickSound This use case begins when the user clicks in the input type menu that he wants to enter the destinations of way points Then as long as he does not press the Cancel button the Set Destination use case is executed in the l
16. onsibilities GPS controller e provides interface for GPS HW e gives position direction velocity and time according to received GPS data RDS TMC controller e provides interface for RDS TMC HW e gives actual traffic data it receives Map module e provides interface to saved maps with supplemented e provides map uploads actualizations via USB e handles map data e provides interface to save the actual route into persistent memory and to load it Position module e saves desired positions saved ones destination position way points e adjusts position according to the map puts the car on the road error correction e gives actual position it remembers it e handles appropriate data Statistics data module e handles all statistics data including user profiles 10 25 Car Navigation System Radim Cebis and Pavel ernohorsk e updates statistics according to changes in position e provides interface for statistics data and user profiles Traffic data module e handles traffic data received via RDS TMC e keeps inner database of traffic data e provides interface for traffic data POI points of interest module e handles all saved POIs e provides POIs uploads actualizations via USB e provides interface for POIs data e keeps list of desired types of POIs to show Route module e computes route according to map traffic way points actual position and destination e keeps track of upcoming changes in direction and provides inter
17. oop but this time the way points are saved into route module instead of calling set destination It finishes when the Cancel button is pressed Cancel button is shown in all the views as mentioned in design decisions and the screen is in map view 15 25 Car Navigation System Radim ebi and Pavel ernohorsk Offer Another Route GUI Voice module Route module I l I OfferAnotherRouteClick i PlayClickSound i ComputeAnofherRoute I I l l I l l l This use case begins when the user clicks on the Offer another route button which will be in the menu which is accessible by clicking Menu icon from the map view It finishes when the request to compute another route was passed to the route module and the screen is back in map view Change Volume T Voice module I I I VolumeUpPress I I PlayClickSound 1 IncreaseVolume Pressing VolumeDown inicializes similar action AN Changes are obvious This use case begins when the user touches volume up or alternatively volume down button It only passes the message to increase decrease the volume to voice module 16 25 Car Navigation System Radim Cebi8 and Pavel ernohorsk Compute route GetActualPosition actualPosition GetWaypointsAndDestination listOfPoints GetTrafficData TrafficData I I GetAdjecentData point
18. r provides services to the layer above it and receives services from the layer below it Components inside one layer can also communicate between themselves This way we can achieve good separation of responsibilities and the components are not dependent on many others Layers of architecture Outer input layer Layer which provides input from outer systems GPS RDS TMC This way the components will be independent from the particular system and usable in other possible projects Data layer 9 25 Car Navigation System Radim Cebis and Pavel ernohorsk Provides all data needed for system activities This way we can separate application logic from data handling and the handling is centralized in one layer providing better control over the data All the components provide interface for their data Computational layer Includes higher level functions Usually demanding computational algorithms which use data layer The components in this layer can be replaced for other or better functionality For example route module can be replaced with updated route module providing better path finding algorithm The layer separates application s logic Components provide high level access to data stored in lower layer User interface layer This layer provides user interface including voice output and graphical input user input This way we can easily change the user interface For example localization or change of voice behaviour Module resp
19. ser can select types of input i e by address coordinates etc m Destination EN Touch E SetDestinationByTouchClick EN pu WaitForMapTouch MapTouch PlayClickSound SetDestination position This use case begins when the user clicks in the input type menu that he wants to enter the destination by touching the screen pointing at the place on the map After every call of SetDestination a new route is computed executed a Compute route use case It finishes when the destination was passed to the route module and the screen is back in map view 13 25 Car Navigation System Radim Cebis and Pavel ernohorsk Set Destination By Address ue Voice module i Ee PlayClickSound EE Continue Touch PlayClickSound OfferDestination partialAddress Retumed info is displayed to user destinations aitForOfferedDestinationSelection OfferedDestinationTouch PlayClickSound SetDestinatipn position This use case begins when the user clicks in the input type menu that he wants to enter the destination by entering the address It includes the offering with selection of found addresses It finishes when the destination was passed to the route module and the screen is back in map view Set Destination By Coordinates ES E34 Voce moa module Roue mede module E NN PlayClickSou
20. the navigation capabilities which require GPS module within at most 5 seconds 11 After turned on device has to be fully operational within at most 3 minutes while on open view or 5 minutes while in the city while GPS satellites are working and in range Responsiveness 12 Map is refreshed while navigating to destination at 20 frames per second including all interactive input like zoom and changing between top view and 3D view Interoperability 13 Maps and points of interest can be updated by standard PC not older than 5 years with appropriate operating system without any additional software 14 Statistics can be downloaded to standard PC not older than 5 years with appropriate 2 25 Car Navigation System Radim Cebis and Pavel ernohorsk operating system without any additional software Functional 15 When the route is recomputed because of diversion the current direction of the car is taken into account and device tries not to force the user to turn around when it is not allowed 16 User can ask for alternative route Alternative route is that one where at least 30 of the route will be different will lead on different roads 17 Car is kept on the road until its position is more than minimal accuracy far from any road then the car is placed on the received position 18 Car its representation will be shown every time on the same place horizontally centred and vertically in the lower one third of the map while navig
21. tion which should be easier to implement Also no drivers are needed in modern operating systems so our system will not need any additional installations e Direction of the car will be remembered and used in path finding algorithm Supports 15 Rationale it will allow us to keep the car representation in right direction and the algorithm will not force the driver to turn when he deflects from the route e Weare using incremental path finding algorithm the alternative route is picked up from other not so well rated routes Supports requirement 16 Rationale alternative route was already computed when the optimal route had been searched and it will always give us different route e Voice module will run as an independent thread which is asking for route changes every second Supports requirement 19 Rationale The system will not be overwhelmed with questions from this module and still it will be fast enough for a driver e Internal implementation of GUI will have customizable colour schemes Supports requirement 22 Rationale this way we can achieve variable user interface and in future we can make it more attractive Also it allows tuning of day night modes e The actual route will be saved in persistent memory Supports requirement 25 e There will be screen which will offer the user possibility to select the type of input for destination Types will be address coordinates selection from previously saved position touch on the map Suppor
22. tistics A N lt lt include set the dest by address set the dest by coordinates ie save actual position set the dest by touch download statistics update maps save POls to device lt lt irclude gt gt Pc 1 at 1 lt lt include gt gt 1 play voice and display notices select types of POI to show show map and info panel create profile update position and time update traffic information GPS RDS TMC This diagram describes all the possible uses of the system Use cases Play voice and display notices and Show maps and info panel are here to warn of the need to process these use cases even without the user s input Some of the use cases are described via their sequence diagrams with commentary 8 25 Car Navigation System Radim Cebi amp and Pavel ernohorsk Component diagram user interface voice module GUI computational layer route module map visualization module statistics controller 1 4 l l Ts BS data layer i T 1 1 i 1 traffic data module map module position module statistics data module POI module L3 includes saved poistion position adjustment according to map outer input A RDS TMC controller GPS controller C4 We have decided to use 4 layers A laye
23. ts requirement 26 Rationale it is better to offer the user a crossing in the interface then overwhelming the interface with too many input graphics components e There will be 20MB of internal persistent memory reserved for statistics last planned route configuration and saved positions Supports requirements 23 24 25 27 28 29 Rationale 640kB ought to be enough for everybody but we believe that for persistent use nowadays 20MB should be enough e Statistics will be stored in the form of csv tables Supports requirement 30 Rationale simple file format which is supported in many applications MS Excel OpenOffice etc e There will be 2GB of place in the device for the maps and POI data files So there will not be problems to load accurate maps of whole Europe Supports requirement 33 Rationale this amount of memory is enough for holding all the relevant data in appropriate radius 6 25 Car Navigation System Radim Cebi8 and Pavel ernohorsk UML Basic Diagrams Context diagram User via car navigation system T User RDS TMC User uses the device in a car User via USB uses the device while uploading new maps POIs and downloading statistics GPS input from satellite system RDS TMC input from radio transmitters 7 25 Car Navigation System Radim Cebi amp and Pavel ernohorsk Use case diagram set waypoints set the dest by saved position reset sta
24. tween the seconds is calculated by interpolating last known values If the RDS TMC message is composed only from compulsory data it takes 68 seconds to receive all the information from the message sent by the RDS TMC transmitter transmitting speed is 1187 5 bits per second maximal number of events in the message is 2048 and one event is composed of minimally 39 bits But the RDS TMC controller will check the reception of new events every second so the database of traffic problems is kept actual Screen will be refreshed at 20 Hz and user input will be noticed at the same rate Computing route can take 3 seconds while the screen is refreshed at 15 Hz Statistics will be updated every second Voice module is retrieving information about direction changes every second Estimated resource consumption Name of the event CPU Usage in percent Operating Frequency of memory usage in occurrences percent Acquiring position from GPS 2 1 1 Hz HW Update of the actual position 4 1 28 Hz including interpolation and error correction Acquiring new data from RDS 2 2 1 Hz TMC Screen refresh and user input 35 25 20 Hz checking 21 25 Car Navigation System Radim ebi and Pavel ernohorsk Computing road while keeping 78 80 Dependant on user s the screen refreshing in 15 Hz needs but at most once per 3 seconds Statistics update 2 3 1 Hz Voice module 10 15 1Hz
25. ystem operations his function might be turned of by the user he can live without it EFFORT how much effort will be needed for implementing this component name of reviewer name of application Radim Cebis and Pavel Cernohorsky Car Navigation System phase 1 implementation effort required 0 very little 7 very much Name of Component 0 1 2 3 4 5 6 7 GPS controller x Position module x Route module x Map visualization module X GUI X Map module X Voice module X brief motivation Just reads values provided by GPS HW as specified by the HW Needs to perform interpolation of position and error corrections It will be hard to choose and develop fast algorithm with best results which must take into account traffic information Depends on graphic interface and hardware Needs fast implementation Depends on the OS API but should not be so hard to implement alone Needs good designed data structures with fast spatial search Depends on underlying sound HW and chosen libraries But should not be so hard 25 25
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