automatically fit as final output for numeric mapping. This necessitates 
interpolations of various kinds (Schut 1976). Numerous researches and 
program developments in this regard have already been undertaken (for 
example, Ebner et al 1980). 
Some of the direct applications of DTM are: Generation of pro 
files, Generation of contour lines, Generation of perspective views, Earth 
work calculations, Terrain simulation, Terrain object models (in plaster) 
and Computer-controlled cartography. Several national mapping organ 
izations, notably in the USA, Canada, FR Germany and Australia are pro 
ducing digital cartographic.data bases. One can reasonably expect that in 
the near future most of the time-critical manual cartographic operations 
’would be superseded by completely automated systems with only the critical 
data-interpretation, judgement and decision making operations requiring 
human intervention. 
Digital mapping based on the DTM concepts and related developments 
is flexible and offers advantages to allow very efficient and cost-effec 
tive mapping particularly by using automated correlation plotters like the 
Gestalt Photo Mapper bv Hobrough (Allarn 1978) and this together w T ith the 
constantly improving computer technology. Such approaches are expected to 
be of great help in the near future. 
6.2.4.2 Real-time Photogrammetry 
The revolutionary technological developments that started in the 
1970s in fields like microelectronics, semiconductor crafts and photonics 
have influenced fundamental new thoughts and researches aimed at obtaining 
better efficiencies in the recording, data processing, data storage and 
administration phases of photogrammetric operations. In computer science, 
a "real-time" system is understood as "the processing of information or 
data in a sufficiently rapid manner so that the results of the processing 
are available in time to influence the process being monitored or con 
trolled" (Sipple and Sipple 1972). 
In view of improving efficiency and with regard to certain time- 
critical operations, in photogrammetry certain "on-line" operations have 
been previously meant to be in connection with the "real-time loops" in 
analytical plotters or the "real-time data transfers" from spaceborne 
sensors. Real-time, however, does not mean zero time. For example, real 
time in the context of data acquisition and data processing is generally 
considered such that the response time of a process must be within one 
video cycle which is between 0.03 and 0.04 second, depending on the video 
standard. On the other hand, real-time performance depends not only on 
the amount of data but also on the complexity of data, type of required 
results, algorithms and hardware used. 
. At a recent symposium organized under the auspices of the ISPRS 
Commission V (Archives 1986, 26/5) one would note that a real-time photo 
grammetric system is meant to process digital images, where the heart of 
the system consists of an image-processing unit. Image enhancement could 
very much be a part of the process. Detection, recognition and information 
extraction are pertinent phases of such systems.