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The choice of components for composition of an information collection system 
includes a wide range of instruments: classical analog instruments, 
stereocompilers, analytical plotters, digitally controlled orthophoto and 
stereo-orthophoto generators; equipment for automation of processes, and an 
assortment of computing devices and interactive display and editing 
facilities. It is evident that, from these components, a number of 
differently configured systems may be built for the achievement of the same 
objective. In principle the choice of processes and the choice of 
instruments for the performance of these processes will depend mainly on the 
constraints imposed by criteria such as the required accuracy and speed, and 
by factors related to the economical constraints and the constraints imposed 
by human resources. In principle, there are two extreme approaches in the 
structural composition of the components. One is based on fully 
decentralized processes where the components are not physically connected and 
there is no possibility for a direct flow of information between the 
components. The other extreme is the fully centralised approach where the 
components are physically connected and the transfer of intermediate 
information between components is an internal transaction. Between these two 
fully off-line and fully on-line structures of the system, there is a number 
of possible configurations of components and sub-systems. Only one of these 
will be optimal for a particular set of constraints. 
In practice the macro structure of the system will normally comprise two 
subsystems: the control densification subsystem and the subsystem for 
compilation of detailed information. The latter subsystem may be further 
subdivided into two parts: one for the collection of information on elevation 
and the. other for. the collection of. information. on. features. (i.e. 
planimetry). : 
A significant influence ‚on the configuration of the information collection 
system will also be the form chosen for the source information record. At 
present, due to the requirements for reliable information of high metric 
quality, the only acceptable input for the control densification subsystem is 
the original analog photographic record acquired by precise, well-controlled 
photogrammetric frame cameras from airborne platforms. For the compilation 
subsystem, besides the original photograph, its derivatives: the orthophotos 
and stereo-orthophotos may be considered. 
The most efficient control densification subsystem is the one based on 
analytical plotters with a special software package for on-line, analytical 
aerial triangulation. If this subsystem is on-line with the main computing 
and external storage facilities of the land information system the collected 
information can be fed directly into these. After the execution of block 
adjustments, the adjusted coordinates of control points and the orientation 
parameters can be stored in "control files" accessible to the analytical 
instruments of the compilation subsystems (i.e. to analytical plotters or 
analytical  scanner-printers for generation of digital terrain models, 
orthophotos and stereo-orthophotos) for restoration of models without the 
repetition of exterior orientation processes (Kratky, 1982). The alternative 
to an analytical plotter based control densification subsystem would be a 
comparator-based subsystem. This subsystem may also be in an on-line 
configuration with the computing and storage. facilities. of. the. land 
information system but the advantages of this configuration are negligible. 
It should be noted that the analytical plotter based subsystem for control 
densification may be readily converted into a compilation subsystem for 
collection of detailed information (by the application software). This 
cannot be done with a comparator-based subsystem for control densification.