. The 
ligital 
. time 
up of 
tional 
isting 
s and 
'ener- 
nakes 
orate 
lating 
round 
paper 
lysis. 
ty of 
treo- 
ogra- 
nage- 
| sub- 
s on 
raphy 
rksta- 
addi- 
urs at 
DEM 
  
d) To analyse the results. 
3. HARDWARE / SOFTW ARE 
CONFIGURATION USED 
a) Inter Map Analytic Photogrammetric worksta- 
tion 
b) IMA SPOT software 
c) Digital Terrain Modelling software 
d) IGDS software 
4. DATA USED 
Data Set A 
1) Stereo-imageries Left Right 
No. 11733 - 055028 11365 - 052654 
View angle + 19.96 - 18.44 
Date of pass 20.11.1990 17.11.1990 
ii) Scale of aerial photography 1: 25,000 
Data Set B 
1) Stereo-imageries Left Right 
No. 11114-055630 11115-053711 
View angle * 15.16 - 18.16 
Date of pass 11.03.1989 12.03.1989 
587 
5. METHOD 
5.1 Data capture for updation : 
Control points were selected at the planning stage 
and it was ensured that the control points used for 
setting up the stereo spot - imageries were se- 
lected in such a way that their identification was 
beyond doubt on maps and stereo-imageries. In 
case of Data set A , the points were also identi- 
fied on aerial photographs. The coordinates of 
control points were readout from 1:50,000 scale 
maps. A number of well spread out check points 
were selected for the subsequent analysis. 
The SPOT stereo-imageries were setup on Inter 
Map Analytic Photogrammetric Workstation and 
were processed for the full solution. A few con- 
trol points configuration were tried till the solu- 
tion converged and was accepted for each data 
set. The models were then evaluated by making 
a through comparision between the map and the 
3-D model of the stereo-imagery. 
Deliberate comparision was made between the 
existing maps and the stereo-imageries and the 
details, not appearing in the map, but which ap- 
peared in the stereo model, were stereo digitized 
as per the pre-determined data structure. 
5.2 Terrain Modelling : 
The stereo SPOT model was used for collecting 
DEM data. The sampling pattern was chosen 
keeping in view the type of terrain. Basically 
there are two methods in which DEM data is 
collected : uniformly spaced points and non- 
uniformly spaced points with X, Y, Z triplets. 
Generally non-uniformaly spaced points have 
more adaptive ability of the terrain. Keeping all 
the factors in view such as type of terrain, purpose 
of DEM, equipement available, processing and 
storage facilities ; the DEM data was collected by 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996