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corrections. 
Digital techniques use digital images and digital processing. A 
combination of both techniques is implemented in hybrid systems, 
using partly analogue and partly digital images in the course of 
processing. 
Analytical, hybrid and digital techniques are versitile and 
flexible. The corresponding systems can be easily integrated into 
larger entities. 
The variety of the systems' architecture, their utilities and 
performances, makes a uniform overall comparative evaluation very 
difficult; hence, partial evaluations seem to be more practical. 
First, however, consideration is given to some significant 
contextual factors that influence the technical evolution. 
Accordingly, the evaluation criteria are stated, and then the common 
features of each technique or system type are studied and assessed. 
Evaluation of the specific features is differentiated according to 
the main production lines. 
Analytical and hybrid techniques have recently reached operational 
maturity. The digital techniques are on the threshold of maturity 
for automatic aerial triangulation and for medium and coarse terrain 
relief modelling. They are also applicable to image transformations, 
such as to orthophotographs. The reduced quality of digital images, 
however, impairs the modelling of terrain features other than 
relief. 
The major potential of digital techniques is their flexibility and 
ease for automation. 
2. CONTEXT 
For a comparative study of the analytical and digital techniques and 
systems, the following contextual factors seem to be most 
significant: 
- New developments in the basic and related fields; 
- The state of the art in GI technology, especially in 
photogrammetry; 
- The techniques for the GI applications in users' domains. 
These factors are mutually related (figure 1). In the following, 
consideration is given to each.