Towards routine large-scale, discrete spatial event simulations

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1 Towards routin larg-scal, discrt spatial vnt simulations Elln-Win Augustijn-Bckrs 1 & Rolf A. d By 1 1 I.T.C., Hnglosstraat 99, P.O.Box 6, 7500 AA Enschd, Th Nthrlands Tlphon: +31 (0) Fax: +31 (0) augustijn@itc.nl, dby@itc.nl 1. Introduction Simulations hav grat potntial as tools to lad to a bttr undrstanding of th world s procsss. Much prvious rsarch on spatial simulations was cll-basd (cllular automata) but mor rcntly, grat advancs hav bn mad in objct-orintd (vctorbasd) discrt vnt simulations. In most of ths simulations th spatial componnt is undrdvlopd. Many discrt vnt simulations ar applid in filds whr th spatial componnt is irrlvant. Thy ar dynamic modls of factoris or manufacturing systms, lvators and othr non-spatial scnarios. Our knowldg of systms and simulations has rachd a point whr objct-basd bhaviours can b dirctly translatd into computabl ruls and usd to gnrat systms. (Bnnson and Torrns 2004). Compard to traditional simulation mthods, objct- or agnt-basd modlling is lss abstract and closr-to-rality, sinc it xplicitly attmpts to modl th bhaviour of individuals (Wagnr and Tulba, 2003). Worboys vn stats that th nxt ral brakthrough in computr modlling of gographic phnomna coms whn w mov from an objct-orintd to an vnt-orintd viw of th world (Worboys, 2005) Existing simulations ar oftn application-orintd. Thy ar not basd on a gnral concptual framwork that allows for intgration with a standard or spatial DBMS and/or Gographic Information Systms. Wagnr and Tulba (2003) argu in favour of th intgration of agnt-orintd modlling softwar and information systms (including GIS) and agnt-basd simulation. Th main objctiv for our study was to gain undrstanding on how to routinly gnrat spatial simulations (agnt-basd discrt vnt simulations) that ar linkd to a standard spatial databas or GIS. This rsultd in a concptual framwork for simulation systm dvlopmnt and a traffic simulation tsting scnario. 2. Concptual framwork Diffrnt filds of rsarch contributd mthods and concpts that wr intgratd in our concptual framwork. Ths includ classical discrt vnt simulation, vnt-basd approachs, gospatial vnt modlling, agnt-objct-rlationship modlling, and objctorintd modlling (Zhou 2006). A simulation has a data modl or static modl (using constructiv gomtry), a bhaviour modl and a dynamic modl (simulation). Th data modl includs th moving

2 and non-moving objcts, in our pilot xampl th road ntwork, cars and travl plans. Th fact that an objct dos not mov dos not imply that it is without bhaviour. An xampl of non-moving objcts with bhaviour is th intrsctions: though thy do not mov, thy ar activ as thy implmnt ruls of priority (which car will cross th intrsction first). Th bhaviour modl hids in th activ class dfinitions. Th bhaviour production systm consists of bhaviour ruls, actions, conditions, mmory rul intrprtrs and arbitrs. Togthr, thy dfin an agnt s bhaviour. Bhaviour ruls xplicitly stor th intraction pattrn by dfining what-if scnarios. Each rul consists of four parts, namly (a) a class nam n, (b) a condition c(s,o), (c) a charactristic a, and a namlss function f(s,o). Th opration of ths ruls has bn coind spatial awarnss, thir application is roughly as follows. An objct s (for slf) is capabl of dtcting which othr objcts o ar in its vicinity; th rul dtrmins how o affcts s s bhaviour. Th rul only has an ffct if n is th nam of o s class and th condition c(s,o) holds. If so, s s charactristic a (spd is th normal xampl hr) is affctd and th ffct is dtrmind as f(s,o). In cas that a is spd, f(s,o) provids us with a suggstd spd for s, du to o s vicinity to s. Objct o will collct all such suggstions from objcts in its vicinity, and thn dcid what to do with thm: With spd it will nxt assum th lowst suggstd spd. Two spcials of narby objcts complt th story: s suggsts to itslf its maximum cruising spd, and th road on which it travls suggsts its maximally allowd spd. This approach is gnric as w allow narby objcts to influnc any charactristic of th objct, givn a condition. Th dynamic modl of a discrt vnt simulation is basd on a chronology of vnts. Each vnt occurs at a tim instant and marks a rlvant chang of stat in th systm. Concptual componnts of such a dynamic modl ar th clock that kps track of simulation tim, and th vnt list. Exampls of vnts in our simulation ar: a moving objct arriving in a nw location, and a traffic light changing light. Each vnt has a tim of occurrnc; th simulation schduls vnts in its vnt list(s). 3. Th prototyp simulation Th objctiv of th prototyp was not to construct a ralistic traffic simulation including all possibl agnts ncssary to modl th complxity of ralistic city traffic. It was mant to dmonstrat th applicability of th concptual framwork, to tst th link btwn th databas and simulation, and to invstigat th ffcts of scaling up th numbr of agnts. Th programming languag usd is Python, in combination with th packag SimPy. First, th simulation was dvlopd as a stand-alon simulation. Aftr initial tsting th simulation was adaptd to allow a connction with our spatial databas. This connction was ndd to load th simulation with a ralistic amount of input data to tst th prformanc of th systm.

3 3.1 Data modl Th data modl or static modl was implmntd with th PostgrSQL/PostGIS spatial DBMS. Th databas systm is usd to stor a singl lan, dirctd singl modal ntwork. It also stors information about moving objcts and thir travl plans, which includ start location, dstination and start tim. Our moving objcts for now modl cars, and ths will start at a givn start tim and location, and will follow thir associatd travl plan until thy rach thir dstination. Each car is associatd with a singl travl plan and this travl plan will rmain unchangd during th simulation. Th ntwork is nabld with an M domain to allow masurmnt along th road sgmnts. This nsurs that th car can start and nd its journy at any position along th road sgmnt. Travl plans indicat on which road sgmnts th car will travl and in which ordr ths road sgmnts will b visitd. Th travl plan also stors information about th dirction in which th car will mov ovr th road sgmnt, diffrntiating btwn th to-from and th from-to dirction. 3.2 Bhaviour modl Only th car, intrsction, road sgmnt and traffic light classs currntly hav bhaviour dfind. Traffic lights bhav indpndntly: thy display priodic chang of light (grn, yllow, rd), but do not hav intraction with any of th othr agnts. Thy ar, howvr, visibl. Th intrsction has intraction with th cars. Th bhaviour of an intrsction is to rgulat th occupation of th intrsction spac; only on car can pass at any tim. It implmnts ruls of traffic priority, and thus it will assign a priority to all waiting cars. It will do this by maintaining a waiting quu and a swrving quu (activ quu).

4 Car Road sgmnt L n g t h R o a d D r i v i n g Rgistr No othr cars rgistrd A d j u s t S p d Othr cars nar Unrgistr R g i s t r c a r s Max spd 50 km /hour Car 1 will rduc spd to 30 km/ hours Spatial awarnss Slowr car Figur 1 (lft) Squnc diagram, (right) cars will adjust thir spd whn slowr cars ar within thir spatial awarnss. Th road sgmnt has intraction with th cars. Bhaviour of th road sgmnts is th rgistration of th location of cars. Each road sgmnt rgistr s all cars along its road at a spcific tim, and whn rqustd provids th information of th position of othr cars so that a car knows which othr moving objcts ar clos and can us this information to adjust its spd or com to a stop in ordr to prvnt collision. Th road sgmnt dos not communicat th last rgistrd position of a car but th position of this car at th rqustd tim. During its journy, a car will possibly mt and intract with othr objcts lik cars, intrsctions and traffic lights, until it rachs its dstination. Th car is th only moving objct that changs its position, has a spd and dirction of movmnt, and intracts with othr cars to adjust its bhaviour. Th spd of th car will vary according to rstrictions imposd by th road sgmnts (maximum spd limit) and th closnss of obstacls. Cars do not activly chang dirction, sinc such changs simply follow from th sgmnts in its travlplan. Chang of spd is implmntd as a stp function, not as gradual acclration or dclration. Concrning th dynamic intraction modl, only cars act intractivly with othr typs of objcts/agnts. Th location of a car will induc it to rqust information from othr objcts/agnts. This bhaviour is th awarnss that nabls an agnt to sns th prsnc of othr agnts in its vicinity and bhav accordingly.

5 3.3 Simulation modl For prformanc rasons, intraction btwn th simulation and spatial databas at prsnt only occurs at bginning and nd of a simulation. At start tim, road ntwork, cars and travl plans will b loadd. At th nd, collctd waypoints for all moving objcts ar rtrivd from th simulation and uploadd to th databas for latr analysis. Figur 2, Intgration of th simulation and DBMS (Karim 2007) 4. Up scaling of th systm In th first phas, our prototyp systm was dvlopd and tstd with only a fw roads and cars. Aftr th connction with th databas th numbr of roads was scald up to approximatly 4000 roads, 250 traffic lights, and th simulation workd with 400 cars. Th prformanc of th systm is good; it taks approximatly 10 sconds to run th simulation with th numbrs of agnts, on a standard Windows XP dsktop machin. 5. Conclusions Th ky tchnology for building discrt vnt simulations for spatial phnomna that intract with gnric DBMS and GIS systms is availabl. An opn sourc programming languag lik Python provids good possibilitis of linking to a DBMS. Th discussd xampl shows th applicability of th tchniqus providd by objct-orintd modlling/programming and discrt vnt thory. Bhaviour ruls provid th possibility of implmnting spatial awarnss that nabls an objct to rspond to othr agnts whn thy occur in its vicinity.

6 6. Rfrncs Bnnson, I and Torrns, P.M. 2004, Gosimulation: objct-basd modling of urban phnomna Computrs, Environmnt and Urban Systms, 28 (1-2): p. 1-8 Karim, F. 2007, Upscaling a spatial discrt vnt simulation with DBMS, MSc thsis, ITC Enschd. Wagnr G and Tulba F, 2003, Agnt-Orintd Modling and Agnt basd Simulation, ER 2003 Workshops, LNCS 2814 pp , Springr-Vrlag Brlin Hidlbrg. Worboys, M, 2005, Evnt-orintd approachs to gographic phnomna, Intrnational Journal of Gographic Information Scinc, Vol 19, no 1, January 2005, 1-28 Zhou, Y.H.,2006, Explorativ rsarch on mthods for discrt spac/tim simulation intgratd with th vnt-basd approach and agnt concpt, ITC Enschd, th Nthrlands.