1. Exploration of Ground Truth from Raw GPS Data National University of Defense Technology & Hong Kong University of Science and Technology Exploration of Ground Truth from Raw GPS Data Huajian Mao 1, Wuman Luo 2, Haoyu Tan 2, Lionel M. Ni 2, Nong Xiao 1 1. State Key Laboratory of High Performance Computing, Hunan 410073, China 2. Hong Kong University of Science and Technology, Hong Kong

2. Exploration of Ground Truth from Raw GPS Data National University of Defense Technology & Hong Kong University of Science and Technology Outline Background Related work Design of TruthFinder Evaluation Conclusions

3. Exploration of Ground Truth from Raw GPS Data National University of Defense Technology & Hong Kong University of Science and Technology Background Map matching – to align the raw GPS data onto the corresponding road network to find out a sequence of road segments to denote that a vehicle has traveled along (ground truth). Ground truth data is important. – to validate the accuracy of a map matching algorithm – to tune and evaluate the effectiveness of various map matching algorithms

4. Exploration of Ground Truth from Raw GPS Data National University of Defense Technology & Hong Kong University of Science and Technology Background In practice, however, there is no (or only a little) ground truth data to validate the calibrated GPS data. Observation – Most of the ground truth path of the trajectories can be correctly identified by human-labeling on the historical raw GPS dataset.

5. Exploration of Ground Truth from Raw GPS Data National University of Defense Technology & Hong Kong University of Science and Technology Motivation Challenges – Pure human labeling costs a lot of time – Pure map matching algorithms cannot keep the precision TruthFinder – Find the ground truth by incorporating traditional map matching algorithms and human intelligence

6. Exploration of Ground Truth from Raw GPS Data National University of Defense Technology & Hong Kong University of Science and Technology Related work Ground truth exploration methods – Datasets collected by driving vehicles ( drive around the city, and periodically record the GPS positions together with the roads where they drive on ) – Human labeled datasets ( find the most likely road segment for each of the GPS records in the trajectory to represent the GPS record is reported from ) – Synthetic datasets ( pick up a path from the road network, periodically select some points on the path, and introduce some errors with normal distribution to generate the synthetic data )

7. Exploration of Ground Truth from Raw GPS Data National University of Defense Technology & Hong Kong University of Science and Technology TruthFinder Principle – to find the ground truth data from historical raw GPS data – to explore the ground truth data by interactively matching the GPS reports which incorporates traditional map matching algorithms and human intelligence in an unified manner.

8. Exploration of Ground Truth from Raw GPS Data National University of Defense Technology & Hong Kong University of Science and Technology TruthFinder Overview of truthFinder system architecture

9. Exploration of Ground Truth from Raw GPS Data National University of Defense Technology & Hong Kong University of Science and Technology TruthFinder Recommendation Preparation Information Presentation Assessing and Tuning Ground Truth Data Exploring

10. Exploration of Ground Truth from Raw GPS Data National University of Defense Technology & Hong Kong University of Science and Technology Evaluation Dataset Road network of ShanghaiLengths of the trajectories

11. Exploration of Ground Truth from Raw GPS Data National University of Defense Technology & Hong Kong University of Science and Technology Evaluation Comparison of operation numbers OP# of TF (HMM) OP# of TF (STM)OP# of EPScratch

12. Exploration of Ground Truth from Raw GPS Data National University of Defense Technology & Hong Kong University of Science and Technology Conclusions We propose TruthFinder, a system of interactive map matching the collected raw GPS trajectory data. It employs human intelligence to aid the map matching algorithms to explore ground truth data from raw GPS data.

13. Exploration of Ground Truth from Raw GPS Data National University of Defense Technology & Hong Kong University of Science and Technology Thank you! Questions? Please contact huajianmao@nudt.edu.cn