310 
Output 
devices 
Fig. 5: Digital system 
A digital system is operated interactively from a work station. A 
work station is equipped with a monitor for display of single images 
or stereopairs, and a simple optical viewer for mono- or stereo 
observation. 
One of the most important items for the comparative study of 
analytical and digital systems concerns the image quality in 
conjunction with the field of view or the size of the displayed 
image window. For image interpretation, it is essential to perceive 
simultaneously the feature of interest and its context. A 
requirement for discerning the primitives of both the features and 
their context is high image quality; this holds especially for small 
terrain features. The field of view (or the window size) and the 
image quality strongly influence the certainty of image 
interpretation. The economics of the photogrammetric modelling 
depends mainly on the interpretability. 
4.3 Software 
The software can be differentiated according to the extensions of 
the system for operating the interactive work station(s), the 
control of the photogrammetric devices, the basic photogrammetric 
software, the software for specific photogrammetric applications, 
the related applications, and the software for support. 
The basic photogrammetric software serves for initiation and 
execution of the basic routines, such as image and model 
orientations, geometric transformations and corrections, and for 
stationary and dynamic restitution. These can be supplemented by the 
graph-image overlay routine. 
The specific photogrammetric application software is intended for 
individual production lines, such as aerial triangulation, terrain