AUTOMATIC PRODUCTION OF DTM DATA BY DIGITAL OFF-LINE 
TECHNIQUE 
B. Makarovic 
Photogrammetric Dept., ITC, The Netherlands 
Commission II, Working Group II-2 
ABSTRACT 
A review is presented of the state of the art in digital off-line 
technique for production of DTMs. Outlined are the main process 
stages, their interactions, and operations involved. Data structure, 
strategy, algorithms, and techniques of image matching are strongly 
interrelated. Performance can be improved by optimising the overall 
process and by carrying out some pre- and post-processing operations 
interactively with human. Moreover, use can be made of multiple sets 
of image data, multi-stage strategy, external data, and of collect- 
ive processing. 
I. INTRODUCTION 
The objective is to present an overview of the state-of-the-art and 
thus new developments in automation of digital terrain modelling by 
using off-line (or time-delayed) techniques. The intense and diver- 
sified developments make a comprehensive review in a short paper 
virtually impossible. Nevertheless, an attempt will be made to out- 
line, discuss, and orderly structure the information. 
Because of various restrictions, the contents are compressed and 
simplified. First some general issues are reviewed, concerning the 
automatic off-line systems. Then a description is given of the main 
process stages, i.e. pre-processing, image matching, and post-pro- 
cessing. Each of these is supplemented by a list of the correspond- 
ing development trends. 
II. GENERAL 
Consideration should first be given to the evolution and general 
trends in automation in photogrammetry, definition of the overall 
photogrammetric process, the main stages of automatic restitution 
and corresponding interactions, types of data, problems originating 
in input images, and properties of on-line versus off-line automatic 
systems. 
l. Evolution 
The first photogrammetric automated systems (analogue, hybrid and 
all-digital) were developed in the period 1958-1962. Until 1968, 
electronic analogue systems dominated and then emphasis was gradual- 
ly shifted to hybrid systems. Since 1976, however, a transition has 
taken place to all-digital systems, operating both in real-time and 
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