Wonkyu Park 
  
Accuracy (RMS, meter 
Smooth region Rough region 
5 
Minimum curvature 39.32m 46.74m 
. 44.37m 
Multiquadric 40.54m 49.66m 
Modified She 39.04m 45.44m 
Table 1. Quality assessments of interpolation schemes performed using automatic stereo matching results. 
  
    
Figure 3. Three-dimensional view of DEMs over 30km x 40km region by Kriging (left) and by Gaussian (right). 
3.2 Optimum interpolation strategy 
Although Gaussian interpolation scheme shows satisfactory results, 
unrealistic elevation, unfortunately, can be introduced in large regions 
where stereo matching fails. This can be explained using the concept 
of ‘center of gravity (COG)' and 'empty center index (ECI)' (Kim ef 
al., 1999). The COG of scattered input points compris es the average of 
two-dimensional coordinates. ECI is the mean distance of scattered 
input points from the center of interpolation. If COG is greater than a 
threshold or if normalized ECI is too far from 0.5, interpolation is 
regarded as failure. 
  
Figure 4. Concepts of 'center of gravity' 
(left) and 'empty center index (right). 
Without correcting for COG, boundaries of matched regions will have incorrect elevation. Even if the COG criterion is 
satisfied but stereo matching fails over a small hill, the hill will not be correctly represented after interpolation. Thus, 
the ECI criterion that may be regarded as a one-dimensional version of COG in radial direction is also needed. The 
result of using COG/ECI criteria exhibits correct boundaries of matched regions. 
  
In summary, due to errors in stereo matching, Gaussian interpolation scheme shows satisfactory results for satellite 
images. Also, to prevent interpolation on large regions where stereo matching fails, COG and ECI within each search 
regions of interpolation are used as a rejection criterion. Through this strategy, DEMs can be effectively generated from 
satellite images. 
| 
  
  
  
  
Scen 
View 
4 EXPERIMENTS AND RESULTS | Acqu 
Table 
We will show experiments with two 60kmx 60km SPOT panchromatic stereo image pairs including ocean, rivers, urban 
and mountain, etc. (See figure 5 and 6). Table 2 shows the scene information on SPOT images used. GCPs are collected The p 
using a GPS receiver whose accuracy is less than one meter. For the quantitative assessment of DEMs, we prepare tW softw: 
truth DEMs: 1) 100m-resolution Digital Terrain Elevation Data (DTED) generated by NIMA, USA. 2) 60m-resolution in oce 
DEM generated from digitized contours produced by National Geography Institute. gener: 
DEM: 
| 
  
708 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B3. Amsterdam 2000.