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ABSTRACT 
The paper embraces two main sections: the general principles, and some selected 
topics. The first part is very general. It deals with the survey and classification 
of the different systems, and reviews digital operations together with the correspon 
ding equipment components. It also presents an outline of overall development 
trends. 
The second part, on selected topics, is devoted to the concept of large scale resti 
tution. This concept comprises the acquisition of digital-terrain-model (D. T. M.) 
data and their further applications. The most comprehensive method of D. T. M. 
data procurement seems to be progressive sampling. This method implies adjust 
ment of point density to the local variability of the terrain. Progressive sampling 
can be implemented efficiently only by means of a stereorestitution instrument 
supplemented by an on-line digital computer. 
A potential application of the D. T. M. data is automatic orthophoto printing. For this 
purpose, both optical and electronic printers can be used. Electronic printers are 
more flexible and efficient than the optical versions. 
Another application, which is non-automatic, is digital mono-plotting. Digital mono 
plotters (D.M. P.) are intended for plotting line maps from single photographs of any 
terrain type, for which D. T. M. data are known. Such systems can be builtup modular- 
ly, e. g. by using existing equipfnent components. The expected merits are increased 
flexibility and substantial operational improvements.