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Gis cience 2010 presentation


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How to detect stops in GPS data? An exploratory spatial data analysis approach

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Gis cience 2010 presentation

  1. 1. Uncovering patterns of movement suspension<br />D. Orellana, M. Wachowicz, H.J. De Knegt, A. Ligtenberg and A. K. Bregt<br />Centre for Geo-Information<br />Wageningen University<br />
  2. 2. Motivation<br />One of the main tasks on movement analysis is to detect the places where moving entities stop.<br />Suspension patterns represent the reduction of speed observed when moving entities stop.<br />
  3. 3. Limitations related with the approach<br />Predefined regions<br />Spatial thresholds<br />Speed thresholds<br />+ Temporal thresholds<br />
  4. 4. Limitations related with observation<br /><ul><li>There are no observations of speed=0
  5. 5. Slow movement may be undistinguishable from inaccurate observations.</li></li></ul><li>Our approach<br /><ul><li>For different kind of moving objects.
  6. 6. No need of spatial and temporal thresholds.
  7. 7. Scale-independent.</li></ul>Developing a method to detect movement suspension patterns for collectives of objects using the spatial association of movement vectors.<br />
  8. 8. Different representations of movement<br />Movement astrajectories<br />Movement as vectors<br />
  9. 9. Spatial association of movement vectors<br />A Local Indicator of Spatial Association (LISA) is used to find spatial clusters of low speed vectors. <br />(LISA) cluster map for under-five mortality rate in Nigeria:O. A. Uthman 2008.<br />
  10. 10. Methodology<br />
  11. 11. Implementation<br />Four datasets representing the movement of different kind of entities:<br />Children playing an urban mobile game.<br />Visitors walking in a recreational area.<br />Trucks delivering cement in a city.<br />Elephants moving in a Natural Park<br />
  12. 12. m<br />- 419 children in Amsterdam<br />- 61782 vectors<br />- 10 secondsfor 6 days<br />55 Clusters:<br /><ul><li>Checkpoints
  13. 13. GameEvents
  14. 14. Pedestriancrossings</li></ul>Urban Mobile Game<br />
  15. 15. - 372 pedestriansvisitingthepark<br />- 141826 vectors<br />- Variable time ratefor14 days<br />Dwingelderveld National Park<br />m<br /><br />152 Clusters:<br /><ul><li>Parkings
  16. 16. Attractions
  17. 17. Facilities
  18. 18. Cross - paths</li></li></ul><li>Trucks in Athens<br />[Theodoridis 2003] <br />- 50 Trucks delivering cement<br />- 111 419 vectors<br />- 30 seconds for 40 days<br />m<br /><br />z<br />252 Clusters:<br /><ul><li>Distributionpoints
  19. 19. Buildingprojects
  20. 20. Trafficjams?</li></li></ul><li>Elephants in South Africa<br />[De Knegt, 2003] <br />m<br /><br />z<br />Å<br />- 5 Elephants in South Africa<br />- 100 337 vectors<br />- 1 hourfor30 months<br />85 Clusters:<br /><ul><li>River banks
  21. 21. Water bodies
  22. 22. Fenced places</li></li></ul><li>Overviewof all experiments<br />Proportion of vectors classified as suspension and number of spatial clusters of movement suspension detected in each experiment.<br />Elephants<br />7%<br />85<br />Trucks<br />32%<br />252<br />Visitors<br />6%<br />152<br />Children <br />18%<br />51<br />
  23. 23. Evaluation of the results<br />In the Dwingelderveld National Park, over 90% of movement vectors were associated to relevant spatial features<br />False Positives: 9.1%<br />Unknown<br />Cross paths<br />Facilities<br />Attractions<br />Parking lots<br />Movement<br />Vectors<br />Vectors classified <br />as suspension<br />100%<br />80%<br />True Positives: 90.9%<br />60%<br />40%<br />20%<br />0%<br />
  24. 24. m  z Å <br />Given a movement dataset, the suspension patterns are spatial clusters of movement vectors that fulfil three conditions simultaneously: (a) having speed values below the average for a given data set; (b) having a positive local spatial association of these speed values; and (c) having a minimum statistical significance score of this association corresponding to an established confidence level.<br /><ul><li>Different kind of objects moving in different landscapes
  25. 25. Different spatial a temporal scales
  26. 26. Without thresholds</li></li></ul><li>Limitations<br /><ul><li>Different of moving entities together.
  27. 27. Large datasets.
  28. 28. Real time.</li></li></ul><li>Future work<br />Contextualisation and interpretation.<br />Temporal association of suspension patterns.<br />
  29. 29. Thank you!<br />Daniel Orellana<br />Centre for Geo-Information<br />Wageningen UR<br /><br /><br />