firstly established relative orientation and generated a relative 
DEM without use of GCPs. We then applied DEM matching 
between the relative DEM and a reference DEM. We assumed 
that a ground point (x,y,z) on the relative frame can be 
matched to the true ground point on the absolute frame 
(X. Y,Z) by adjusting their position and attitude and that the 
transformation equation can be generalized as the following 
equation(1), where 5 is a scale factor, R is a rotation matrix and 
(AX,AY,AZ) are shift vector between the two DEMs. This 
equation is different from that of perspective images in that the 
rotation and shift parameters are not constant(Kim and Jeong, 
2011). From DEM matching, we estimated the parameters for 
the equation. 
X X AX (t) 
and they were used only to assess the accuracy of absolute 
orientation through DEM matching. 
  
Figure 1. SPOT-5 stereo pair over Daejeon, Korea 
  
Y |=sR@)| y |+| AY (®) 
Z 
z) (AZ) 
(1) 
Table 1. The properties of the SPOT-5 stereo pair used. 
  
  
In our previous study, SPOT-5 stereo image at a resolution of 
2.5 meter and the reference DEM at a resolution of 30 meter 
were employed for experiments. Relative orientation was 
established from SPOT-5 stereo images with only the image tie- 
points and the DEM grid points(Kim and Jeong, 2010). A 
relative DEM at 10m resolution was generated based on the 
relative orientation. DEM matching was applied between the 
relative DEM and the reference DEM and we could show the 
DEM matching can be used for bias compensation of linear 
pushbroom images without ground control points. 
Here, we improve upon the previous study in two aspects. 
Firstly, we test an accuracy of the DEM matching with different 
number of grid points and perform tests using automatically 
extracted gird points. We will check whether automatic DEM 
matching can be accomplished for absolute orientation of 
pushbroom images without manual extraction and visual 
checking of grid points. Secondly, we extend our experiments to 
the publically available DTED at grid spacing of 90m for DEM 
matching. We validated the feasibility of this dataset for DEM 
matching. 
3. DATASET USED 
For experiments, we used SPOT-5 HRG with 2.5m resolution 
as high resolution satellite images and used two reference 
DEMS, one at 30m grid spacing and DTED at 90m grid spacing. 
Figure 1 presents SPOT-5 stereo pair over Daejeon, Korea used 
and Table | presents their properties, respectively. Figure 2 
shows two reference DEMs over Daejeon area. GCPs for the 
each image were obtained by differential GPS measurements 
  
  
  
  
  
  
ID Left Right 
Sensor SPOT-5 SPOT-5 
Spatial Resolution 2.5m 25m 
Date of Acquisition 20 Dec 2003 11 Dec 2003 
Tilt angle 18.49* -25.53? 
No. of GCPs 18 18 
  
  
  
  
  
Figure 2. Two reference DEMs, one at 30m grid spacing(left) 
and DTED at 90m grid spacing(right). 
4. DEM MATCHING RESULTS 
4.1 Automated DEM Matching 
In this section, we firstly compared the accuracy of absolute 
orientation from DEM matching according to the number of 
Table 2. Accuracy of the absolute models from DEM matching with different number of grid points 
  
  
  
  
  
  
a The No. of grid points Left model errors(pixel) Right model errors(pixel) Object space errors(m) 
ensor ; 
for matching Col Row All Col Row All Horizontal | Vertical 
211 (visual checking) 0.56 1.08 1.21 1.27 1.57 2.02 3.85 3.97 
303 (visual checking) 0.62 0.93 1.12 1.36 1.32 1.89 3.65 3.76 
SPOT-5 
411 (visual checking) 0.58 0.90 1.07 1.28 1.20 1.75 3.45 3.82 
5985 (automation) 0.62 2.12 2.21 1.41 1.66 2.18 5.30 3:98 
  
  
  
  
  
  
  
  
  
  
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