Figure 1. Scheme of location of high resolution images and 
medium resolution images 
The task is to restore the exact location of point M on the left 
image of stereopair (ml). For this purpose a terrain model is 
built from the stereopair but exterior orientation of the model is 
not performed. That is, there is built a free model arbitrarily 
oriented in geodetic space. In this case a specific feature of this 
stereomodel is that it is built from images with different spatial 
resolutions. 
For the images of stereopair from coordinates of the same 
points under the coplanar condition 
Ro x (R; x R2 )=0 (1) 
there are determined the elements of relative orientation (for the 
left image: Alphal, Omegal=0, Kappal, for the right image: 
Alpha2, Omega2, Kappa2). 
4. TRANSFER OF CONTROL POINTS FROM HIGH 
RESOLUTION IMAGE TO MEDIUM RESOLUTION 
IMAGE 
On the first step recognition of control points is made on high 
resolution image. For each control point I we obtain a set of 
coordinates X;, y;. 
On the second step a local DEM is built for neighborhood of a 
control point. Since exterior orientation of the stereomodel was 
not performed then the DEM will be obtained in a free 
coordinate system.. 
On the third step for each control point we determine its 
coordinates in a free coordinate system of the stereomodel 
(Lobanov, 1984). For connection of coordinates on high 
resolution image and coordinates of free stereomodel we can 
write down the following: 
X-Xya=(Z-Zs2)*X/Z' (2) 
Y-Yo-(Z-Z3)* Y'IZ 
IAPRS & SIS, Vol.34, Part 7, “Resource and Environmental Monitoring”, Hyderabad, India,2002 
where 
X'=a,(x-Xo)+ax(y-yo)-a3 f> 
Y'=b,(x-xo)+b2(Y-Yo)-b3 fa 
Z'=c,(x-xo)+C2(Y-Yo)-C3 fa 
Since the Z coordinate of a control point is not known 
accurately then the coordinates are determined by an iterative 
method. At the first iteration Z coordinate is set to some 
average height value. At the next iteration the height value is 
corrected from the obtained X, Y coordinates and local DEM. 
And so on until the error in coordinates becomes lower then the 
required threshold. 
On the last step we perform recalculation of coordinates of a 
control point from the coordinates of free model to the 
coordinates on medium resolution image using the following 
formulas: 
X-Xo= - f,*X"/Z" (3) 
y-yo= y nY'z ; 
where 
X'za,(X-X,i)*bi(Y-Y.,)*ci*(Z-Z.4) 
Y'zay( X-X,i)tbx(Y-Y,1)c2*(Z-Z,1) 
Z'=a3(X-X51)+b3(Y-Y;1)+€3*(Z-Zs1) 
The described technique allows to take into account the terrain 
height (which is not allowed by other methods using 
polynomials) for each control point and hence highly increase 
the accuracy of transfer of points from a high resolution image 
to a medium resolution image. 
5. CONCLUSION 
Solving of the problem of increasing of accuracy of exterior 
orientation of TK-350 images is provided by substitution of 
direct exterior orientation of images using control points with a 
two-stage process: (I) relative orientation of images of 
stereomodel and (ii) transfer of control points to a medium 
resolution image. It is proven practically that the accuracy of 
relative orientation is significantly higher than the accuracy of 
exterior orientation. The remainder vertical parallax can be 0.01 
pixel that is in case of pixel size corresponding to 10m on the 
ground the accuracy of orientation is O.1m For exterior 
orientation of a high resolution image the accuracy can be 1-1.5 
pixel. That corresponds to 2 —3 m for 2m resolution KVR-1000 
images and to 1 — 1.5 m for 1m resolution IKONOS images 
accordingly. Thus, the resulting accuracy of exterior orientation 
of TK-350 images is determined by the accuracy limit of 
orientation of a high resolution image and can equal from 1 to 3 
meters on the ground. 
REFERENCES 
[m 
A.N.Lobanov, Photogrammetry, Moscow, “Nedra”, 1984. 
2. S.YuZheltov, A.V.Sibiryakov, Adaptive Subpixel Cross- 
Correlation in a Point Correspondence Problem // Optical 
3D Measurement Techniques, Zurich, 29 September- 2 
October 1997, pp.86-95.