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4.4 The Purdue Project 
The Purdue images cover the campus area in West Lafayette, Indiana. The neat area from the corresponding images was 
extracted and examined as illustrated in Figure 5. 
  
  
  
  
  
Figure 5. Left and Right Images from Purdue Pair 
This area contains small and large buildings, abundant walkways, and parking lots. There are also some occlusions, 
shadows, and moving objects. The original photographs were nearly vertical and their nominal scale was 1:5000. They 
were originally scanned into digital form with a resolution of 15 micrometers. Their aggregated version at level 2 (30 
micrometers) was employed in this experiment, so one pixel represents approximately 0.3 m. in the object space. 
The straight line, plateau, and spike features were extracted from both images. About 140 epipolar lines covering the 
whole area were examined. There were approximately 50-70 extracted feature points from each epipolar line. However, 
only 35-40 correspondences were found from each set. Some false alarms and missed detections of match pairs still 
occurred. These errors are caused by the imperfect results from the feature extraction process, occlusions and other 
factors. The 3D information computed from feature matching was used as constraint information in the signal matching 
process. 
Searching in the signal matching process was performed independently in two directions, north-south and east-west as 
shown in Figure 6. 
  
  
Figure 6. Orientation of the Vertical Planes Defining the Cost Matrices 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B3. Amsterdam 2000. 271