x We 
on the other hand the effort necessary for field survey operations. Considering 
the financial implications such as unnecessary high cost of photogrammetric 
operations if too large a photoscale is used, or probably still more important, 
the excessive cost of field survey if too small a photoscale is employed, special 
attention should be paid to the problem of semantic information models. 
2.8. identification of consirainis 
Attention should also be paid to the fact that the planner is to a certain degree 
limited in the choice of process components currently available. 
Three such categories of constraints can be distinguished. 
a) Only those process-components, which either are or can ‘be made available 
to the executing organisation, can be employed. Hereby temporary conditions 
in the executing organisation have also to be considered such as the distribu 
ion of the work load over various divisions, temporary underemployment etc., 
resulting from the totality of projects under hand. 
b) Certain specific characteristics prevailing in the project area (e.g. topo- | 
graphic configuration, vegetation coverage, meteorological conditions etc.) | 
might be incompatible with the employment of certain process-components 
Ne. 
c) Certain process-components applicable’ for the execution of different functiona 
| 
phases might be incompatible with one another 
2.9. A simplified model of the design process 
Based on the foregoing analysis and the concepts developed, a model of the design 
process (i.e. the choice of process parameters) can be presented in schematical 
form (fig. 10). Obviously it represents an optimization problem. The ‘objective 
of optimisation might either be a minimisation of cost or of the time required for 
execution or a suitable combination of both. 
The primary input for the design process are the product specifications. The most 
important items of the product specifications affecting the choice of project 
parameters are: 
The type of product required; 
The requirement for qualitative information; 
The type of height information required; 
The planimetric accuracy required; 
The height accuracy required. 
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