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USING SENSECAM TO PURSUE “GROUND TRUTH” FOR GPS TRAVEL SURVEY

USING SENSECAM TO PURSUE “GROUND TRUTH” FOR GPS TRAVEL SURVEY. Li Shen and Peter Stopher Institute of Transport and Logistics Studies The University of Sydney. Ohio, May 2013. 14 th TRB Transportation Planning Applications Conference. Background. GPS Travel Survey.

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USING SENSECAM TO PURSUE “GROUND TRUTH” FOR GPS TRAVEL SURVEY

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  1. USING SENSECAM TO PURSUE “GROUND TRUTH” FOR GPS TRAVEL SURVEY Li Shen and Peter Stopher Institute of Transport and Logistics Studies The University of Sydney Ohio, May 2013 14th TRB Transportation Planning Applications Conference

  2. Background GPS Travel Survey Global Positioning System (GPS) technology has been used in travel surveys since the late 1990s. GPS devices could correct the trip misreporting issue caused by respondents and improve the accuracy of travel data. • GPS ≠ GroundTruth • Signal loss • Signal noise

  3. Ground Truth Ground Truth in Travel Surveys • Reflect real trips • Validate GPS data processing results (i.e., accuracy) • Used for learning system for GPS data processing Approaches to obtaining ground truth • Prompted Recall (PR) survey • Experiments • Visual data (images, videos, etc.)

  4. About SenseCam • SenseCam (supported by Microsoft) is a passive digital camera which contains a number of different electronic sensors. • Takes about 3000 photos per day • Time stamped and battery lasts for 18 hours/day • Stores 8‐10 days of data Certain changes in sensor readings can be used to automatically trigger a photograph to be taken. If nothing changes, it takes photos every 50 s.

  5. Travel Mode

  6. Activity (Trip purpose)

  7. Data • Purposes of This Study • Use SenseCam and GPS devices to pursue ground truth • Understand GPS devices’ performance based on the ground truth • Data Collection • 12 volunteers in Oxford (3-day survey in Oxford) • 7 volunteers in Sydney (5-day survey in Sydney) • Volunteers were asked to carry both SenseCam cameras (provided by University of Oxford) and GPS devices (provided by the University of Sydney) • Data Processing • GPS: G-TO-MAP + Manual map editing • SenseCam: SenseCam Browser + Manual image editing

  8. Comparison for Sydney Survey (1) Trip Comparison (based on start/end time and travel duration)

  9. Reasons for GPS data missing Comparison for Sydney Survey (2) Reasons for failing to split trips

  10. Comparison for Sydney Survey (3) for Sydney Survey (2) Travel Mode Comparison Trip Purpose Comparison

  11. Comparison for Sydney Survey (4) Mode distributions of all trips and missing trips in GPS

  12. Summary • SenseCam can help find the “ground truth”. • SenseCam can help understand the GPS device’s performance in travel data collection. • GPS data missing is more likely to happen • at the beginning of a trip • for short duration trips • Trips recorded in the GPS devices may be split • when a short duration trip occurs at the beginning/at the end of the whole journey • when a short duration activity occurs during the whole journey • Missing trips are more likely to be walking trips.

  13. Questions and Discussion Li Shen, Institute of Transport and Logistics Studies, The University of Sydney E-mail: li.shen@sydney.edu.au Peter R. Stopher, Professor Institute of Transport and Logistics Studies, The University of Sydney Email: peter.stopher@sydney.edu.au 14th TRB Transportation Planning Applications Conference Ohio, May 2013

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