Robert Collins, Chris Jaynes, Yong-Qing Cheng, Xiaoguang Wang, 
     Frank Stolle, Howard Schultz, Edward Riseman and Allen Hanson,
"The Ascender System: Automated Site Modeling from Multiple
Aerial Images,"
Computer Vision and Image Understanding (CVIU),
Vol.72(2), November 1998, pp.143-162.


The Ascender system acquires, extends and refines 3D geometric site models from calibrated aerial imagery. To acquire a new site model, an automated building detector is run on one image to hypothesize potential building rooftops. Supporting evidence is located in other images via epipolar line segment matching in constrained search regions. The precise 3D shape and location of each building is the determined by multi-image triangulation under geometric constraints of 3D orthogonality, parallelness, colinearity and coplanarity of lines and surfaces. Projective mapping of image intensity information onto these polyhedral building models results in a realistic site model that can be rendered using virtual "fly-through" graphics.

As new images of the site become available, model extension and refinement procedures are preformed to add previously unseen buildings and to improve the geometric accuract of the existing 3D building models. In this way, the system gradually accumulates evidence over time to make the site model more complete and more accurate.

An extensive performance evaluation of component algorithms and the full system has been carried out. Two-dimensional building detection accuracy, as well as accuracy of the three-dimensional building reconstruction, are presented for a representative data set.