Robert T. Collins, Yanghai Tsin, J.Ryan Miller  and Alan J. Lipton,
"Using a DEM to Determine Geospatial Object Trajectories,"
Darpa Image Understanding Workshop, Monterey, CA, November 1998.  

Also CMU Robotics Institute technical report CMU-RI-TR-98-19, July 1998.

Abstract

This paper addresses the estimation of moving object trajectories within a geospatial coordinate system, using a network of video sensors. A high-resolution (0.5m grid spacing) digital elevation map (DEM) has been constructed using a helicopter-based laser range-finder. Object locations are estimated by intersecting viewing rays from a calibrated sensor platform with the DEM. Continuous object trajectories can then be assembled from sequences of single-frame location estimates using spatio-temporal filtering and domain knowledge.

Full Paper

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