Problems in Obtaining and Processing of Photogrammetric 
Data for Digital Terrain Models 
Summary 
First, a definition of a digital terrain model is given. 
A number of these models have been developed to obtain 
optimal road designs in a fast and efficient way without 
the need to re-measure the terrain for each alignment 
variation. An example using three terrain classes demon- 
strates how different and dependent on the shape of the 
terrain the most efficient photogrammetric measuring 
techniques can be. In order to simplify the task of the 
operator on the stereo-restitution instrument, a pre- 
interpretation under a mirror-stereoscope will indicate 
what should be measured in the model and in which way. 
Even so, a systematic training of the operator for this 
task will be required. The use of the digital terrain 
model will confront the instrument makers with problems 
concerning faster registration of machine coordinates and 
the automatic transformation of contour lines to digital 
point data. The aim of the Working Group IV/V shall be to 
point out and discuss these questions arising from the 
practical application of digital terrain models. 
Résumé 
On donne tout d'abord une définition du modéle digital de 
terrain. Plusieurs types de tels modéles ont été dóvelop- 
pés pour les buts de planification, avec comme dessein 
l'obtention rapide des conditions optimales de projets de 
route sans le recours continuel à de nouvelles données. 
On montre sur l'exemple de trois catégories de terrain 
combien le mode de mesurage photogrammétrique le plus 
rationnel diffère et dépend des formes du terrain, pour 
la représentation par voie digitale. En vue de faciliter