Multi-scale Windowing over Trajectory Streams

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1、Multi-scaleWindowingoverTrajectoryStreamsKostasPatroumpasSchoolofElectricalandComputerEngineeringNationalTechnicalUniversityofAthens,Hellas16October2012SeCoGIS’121GeoStreaming•Geospatialstreamsderivedfromreal-timedataacquisition•geosensors~vectordata•imag

2、ery/satellite~rasterdata(mostly)•Interestonmonitoringlocation-awaremovingobjects:–numerousvehicles,people,merchandise,animals,...•PRESENTrecordtheircurrentlocation•PASTmaintainhistoricaltrajectories•FUTUREpredictroutes/estimatetrends•Streaminglocations

3、fromGPS/RFID/GSM…–timestamped,georeferencedpointsposechallenges:consumefluctuating,intermittent,voluminouspositionalupdatesprovidetimelyresponsetospatiotemporalContinuousQueries(CQ)overcomelackofsuitableoperatorsintraditionalDBMSTowardsanewprocessingp

4、aradigm:GeoStreaming–queryevaluation–in-memoryindexing–datareduction/approximation16October2012SeCoGIS’122WindowingoverDataStreams•Continuousqueriesevaluatedagainststream“chunks”–Infeasibletoretaintheentirestream“history”•foronlinecomputationinmainmemory,

5、notdisk-boundstorage–Windowsprovideatemporary,boundedportionofastream:•Sliding•Tumbling•Partitioned•Landmark…–Typicallyslidingwindowsinherentincontinuousqueries:•CQ:“every10minutesSELECTAVG(S.temperature)getaveragetemperatureFROMS[RANGE30MINUTESoverpast30

6、minutes”SLIDE10MINUTES]102030405060t16October2012SeCoGIS’123An“Amnesic”Approach•Handlingtrajectoriesofmovingobjectsonline–Doweneedalldetailsofeachhistoricaltrace?•Significanceofeachisolatedpositionistime-decaying•Recentpositionsarefarmoreimportant•Olderse

7、gmentsmaybecompressedorevenpurged•Introducemulti-scalewindowingovertrajectorystreams–Focusonmotionovervaryingtimehorizonsinthepast•Graduallycoarserrepresentationsovergreatertimeperiods•Higherprecisionreservedformostrecentsegments•Coreideaextendsmulti-gran

8、ularwindows[TIME’10]–Novel“scale”semanticsfortrajectorysimplification•Obtaingeneralized,comparabletracesforquerying•Conveyreliablemotioncharacteristics•Nomatterthereportingfrequencyfromobjects16October2012SeCoGIS’12