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relief modelling, image transformations and terrain features 
modelling (other than relief). There are several variants for each 
of these lines. 
The related applications software comprises two main parts, i.e., 
the input-related and the output- related parts. The first part 
addresses production engineering, such as project planning, cost 
calculation, prediction of performance, etc. The output-related 
software concerns GI conditioning for the intended user. Examples 
are GI base formation, various DTM conversions, graphic output, 
calculation of areas, volumes, distances, azimuths, slopes, etc. 
The support software serves fcr the overall system support. It 
contains routines for system testing and calibration, instructions 
for operation and support, etc. 
The difference in software of the analytical and digital systems 
concerns the image processing. In analytical systems, the photo 
stages and/or the optics are positioned mechanically, usually by 
digital servomechanisms. In digital systems, however, a search is 
made for conjugate image windows in the storage device for the 
display on the monitor. The display is aided by the routines, such 
as for image roaming, zooming, and sometimes for image rotation. 
These require very high speed, especially when image resolution is 
high. 
Common software modules can be used for image preprocessing, such as 
filtering, segmentation and resampling. The software for main 
processing concerns the matching, analysis and understanding of 
images. The software for postprocessing serves for conditioning the 
raw output from the main processing, such as image enhancement, edge 
editing, etc. 
4.4 Procedures 
Although the procedures are to a great extent determined by the 
software, they also concern the non-automatic man-machine 
interactions. A procedure is a model of a process reflecting the 
selected methods and means. 
A distinction can be made between the common and the specific 
procedures. The common procedures concern the common routines, such 
as image orientations, transformations, corrections, calibrations, 
image matching, etc. The specific procedures address the specific 
operations of each production line. 
Most of the required processes can be implemented in different ways, 
i.e., by different procedures. The overall procedures are composed 
of the partial procedures; each of these pertains to a main process 
stage in a production line. The main stages can be further branched 
into more specific partial procedures (figure 6). Thus the 
procedures, including the software, can be structured 
hierarchically.