and nght) and with image matching techniques and 
taking correlation between conjugate pixels, we can 
create a DEM. However, in this project since our aim 
was not creating DEM, but using it for different 
purposes, we used an existing DEM of the area that had 
already been created from digitizing contour lines in 
map and it was georeferenced and covered all our area 
of interest and thus we used this existing DEM . 
3.3 Extraction of topographic data from 
scanned aerial photos 
3.3.1 Scanning photos and format conversion. Aerial 
photos were scanned, to convert analog data into digital 
raster form. The required scanning resolution was 
chosen to suit both accuracy and storage capacity. Thus, 
the resolution of 100 dpi was appropriate. The raster 
data was in the TIFF format, therefore, in order to be 
used in the ILWIS system, it should get converted to 
MPD and MPI formats. The Data Conversion program 
was used for this process. 
3.3.2 Radiometric correction . Sun angle correction is 
not applicable since we had only one channel 
information per scene. In this particular case, therefore 
only linear stretch was applied. For haze correction, we 
just shifted the brightness histogram of scanned photos 
to Zero. 
3.3.3 Creation of orthophoto. From the beginning, our 
area of interest was well defined in terms of both X- and 
Y- coordinates so only two scanned photos covered the 
whole area. therefore, the 2 orthophotos had to be 
created. For this matter, the planimetric coordinates 
were interpolated from existing map. 
3.3.3.1 Selection of Ground Control Points (GCP). 
For a good georeferencing, GCPs need to be well 
distributed all over the image. For that matter, tie points 
are selected in the overlapping area. The 1:25000 map 
was used to acquire the coordinates of the well-defined 
points on both the map and photographs. The list of 
GCPs is shown in figure 3 for photo 36 and 37. 
3.3.3.2 Orientation of scanned photos. ORIENT 
program performs an inner orientation based on the 
given relation of the fiducial marks provided the 
following data are given: 
1. Control point file 
2. Patched DEM file 
3. Calibrated focal length 
The transformation file will be delivered as output. 
3.3.3.3 Formation of orthophoto. Once the orientation 
is satisfactory, the patched DEM, the patched scanned 
image, the output orientation files are required by 
ORTHOPHoto program. The output image is still patch 
form. Thus it has to be unpatched which will deliver 
already to display digital orthophotos. 
  
  
  
538 
  
T36N.DAT iu 
pn Col Line x y use nameesg 
1 845 461 0.115 0 1 east. 
2 430 876 0 -0.115 1 south 
3 20 457 -0.115 0 1 west 
4 436 42 0 0.115 1 north 
-1 
pn x X Y use 
1 767.0 878.0 840338.0 3173500.0 1 
2 300.0 794.0 838525.0 3173638.0 1 
3 45.0 599.0 837450.0 3174500.0 1 
4 20.0 94.0 837250.0 3176575.0 1 
5 499.0 39.0 839300.0 3176863.0 1 
6 759,0 183.0 840375.0 3176250.0 1 
7 828.0 416.0 840650.0 3175288.0 1 
T37NN.DAT 
pn Col Line X y use namees$ 
1 845 449 0.115 0 1 east 
2 428 863 0 -0.115 1 south 
3 19 443 -0.115 0 1 west. 
4 436 30 0 0.115 1 north 
~1 
pn X X Y use 
1 667.0 771.0 838525.0 3173638.0 1 
2 395.0 575.0 837450.0 3174500.0 1 
3 217.0 792.0 836713.0 3173625.0 1 
4 189.0 497.0 836550.0 3174800.0 1 
5 360.0 74.0 837250.0 3176575.0 1 
6 725.0 185.0 838813.0 3176150.0 1 
figure 3- GCP file 
3.34 Clipping and Merging. After creation of 
orthophoto, both orthophoto 36 and orthophoto 37 were 
merged. The beginning of column of each orthophoto 
was removed to avoid some darkness after mosaicking. 
With the program MERGE, both orthophotos were 
merged together and meanwhile we defined an area of 
interest from the map and scanned photographs. 
3.3.5 On screen digitizing and Editing. The displayed 
raster image on the screen, without using any hard copy, 
identified features were being digitized directly in the 
forn of point and vector. With the advantage of 
zooming in and out, the cursor movements are adapted 
to the whole screen and the cursor becomes sensitive 
because of following the coordinates of the map placed 
on the digitizer. Several possibilities have been 
introduced with respect to the digitizer set up and the 
digitizing colors and even the existing codes are 
displayed when the user decides to change the mask and 
the codes of the segments. Thereafter, all the digitized 
data in the segment mode, are polygonized in order to 
make closed polygons. For this process, a unique 
number is assigned to each polygon according to the 
landuse separation. 
4. IMPROVED CLASSIFICATION 
4.1 Geometric correction 
The following steps have be done: 
- Patching the radiometrically corrected satellite images 
by use of PATCH program, since RAM does not have 
sufficient space to handle the whole image: 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996