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35 
e automatic obtaining digital 
geographical model (DGM) for 
use in orthophototransforming 
process. 
High speed of image regeneration 
regardless of the size of stereopair 
file allows to gain an efficiency 
in raster-image processing. All that 
allows to pass from one part of 
stereopair to another practically in 
a moment and to change the image 
scale on the monitor. screen. 
Changing the scale of an initial 
digital image is realized in a 
discrete way with coefficient 2 in the 
direction of both reduction and 
enlargement. In the last case screen 
image is formed from the points 
which are the result of interpolation 
of an initial matrix. Images like 
that allows to be processed with 
subpixel accuracy. 
Correlational processing digital 
images is realized in two 
modifications: 
1. two-dimentional correlation for 
points identification during 
relative orientation of 
photographs; 
2. one-dimentional correlation for 
creating a digital geographical 
model (DGM). 
In the first case operator only picks 
out some zone for the points of 
relative orientation, but precise 
identification is realized 
automatically. In the second case 
transformation of an initial digital 
241 
photograph onto a surface parallel 
to the survey base is accomplished 
at the begining. Only then there will 
be no vertical parallax along all 
the stereopair area regardless of 
terrain relief. It allows to use fast 
algorithm of = one-dimentional 
correlation. Raising the accuracy of 
identification is achieved by 
reduction of pixel - element of 
resolution - at the expense of 
dinamic interstepper division up to 
1/8 of pixel. 
Authencity of restoring relief is 
checked automatically according to 
the correlation coefficient of each 
point. When the coefficient is 
coming down below a definite level 
this point is either struck off the list 
or identified by operator. 
Throughput of used algorithm is 
illustrated by the following data: 
DGM with | mm-step in the 
photograph scale (about 17.000 
points) is restored for 20 minutes 
and, by the way, all errors satisfy 
the demand for making 
orthophotoplans for unbuilt 
territories. 
DPS software has been created for 
two operating systems: MS DOS 
and Windows NT/Windows 95. 
(MS DOS and Windows are 
registered trademarks of MicroSoft 
Corp.) 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B2. Vienna 1996