is 
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ive 
nd- 
1). 
DTM 
be 
ub— 
the 
23— 
the 
on, 
ce, 
wly 
uch 
lue 
ing 
ial 
ion 
cal 
E., 
ata 
tal 
the 
nearest DTM points can be identified and used for interpolation. The 
latter can be avoided if the overlaid grid is sufficiently dense. Any 
image point can then be assigned the height of the nearest DTM grid 
point. The grid density can be made dependent on the radial distance 
from the nadir point and the specified accuracy. 
— Differential height of the object points from the DTM surface can be 
acquired by parallax measurement parallel with the measurement of the 
planimetric features (figure 5). The heights Zn obtained from DTM are 
first corrected accordingly (dh) and are then further used for the 
"image-to-model" transformation (figure 8). 
X CONTROL DATA NS a“ 
y 
\Orientat ion\correct ion\ X, 
  
CONTROL_DATA 
dh DTM 
     
  
„a 
  
  
| 
IMAGE TO MODEL 
TRANSFORMATION 
  
  
| 
  
  
  
  
NI 
Nl 
X,Y 
  
  
  
Th no 
  
X,Y | INTERPOLATION 
  
  
  
— yes 
MODEL TO MAP 
(or ground) 
TRANSFORMATION 
  
  
ee == = a em = — — SE 
  
  
  
  
Fig. 8: Image-to-model transformation with óh included. 
Further refinement is attained by automatically assigning differential 
heights to a specified series of successive object points. Hereby dif- 
ferential height can be constant or variable, i.e., interpolated between 
adjacent pairs of object points for which differential heights were 
measured [9]. 
IV INFORMATION AND DATA 
Among the very important issues of integrating data bases are the struc- 
ture, compatibility and description of the information and data. In the 
following some consideration is given to structuring because the struc- 
tures tend to provide a frame of reference for compatibility and 
description. 
Suitable entries (or influencing factors) for structuring information and 
data are: 
— The overall system context (in a broad sense) 
- Destinations (or role) of information and data in the system 
— Process stages (or the states of input and output) 
— Domains of information 
— Specific context of the data base (or its use) 
In the following, an outline is given of each of these main factors. 
35