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The main advantage of the method over alternatives involving physical 
meetings is the lower cost. A much wider international WG can be 
involved at a very reasonable cost. As all members of the WG are 
volunteers the motivation level is high and much work is done in 
members own time. It has been found that an occasional telephone call 
or a visit can stimulate the WG when the more abstract ideas need 
clarification. 
Early work. The WG was formed early in 1979 and the 1st circular issued 
in May 1979. Unfortunately shortly afterwards key members of the ITC 
inner group were obligued to stop work on the project because of the 
pressure of other duties (*) at ITC and in effect the project went on 
ice until mid 1981 when active work restarted. 
The 1st circular proposed a plan for the establishment of cost models 
which envisaged collecting data for production processes over a wide 
spectrum of the surveying and mapping scene. When the response to the 
1st circular was analysed it was very clear that if we had dealt with 
so many production processes simultaneously we would have created an 
information explosion and meaningful analysis would have been very 
difficult if not impossible. As a result when active work restarted in 
mid 1981 a phased approach was proposed and accepted by the WG. 
The phased approach. To be able to manage the considerable amount of 
data that will be generated, the mapping process has been split into 
basic phases which are essentially self-contained and each will be 
handled separately. The following basic phases will be considered: 
stereo plotting (conventional and digital) 
primary data acquisition (aerial photography and auxiliary data for 
mapping purposes) 
aerial triangulation 
field survey (ground control including signalization, field 
identification, completion and verification) 
photomap production (orthophoto and conventional rectification) 
cartography (including reprographics and printing) 
For each phase funtional production processes will be identified 
together with all cost generating sub-processes for technological 
alternatives. The individual cost generating sub-processes will be 
identified in such a way that all possible combinations of rates can be 
recombined and the resulting aggregated values should be of maximum 
benefit to individual organizations and to the photogrammetric 
community as a whole. 
If one takes, for example, the orientation process from the stereo 
plotting phase, the orientation process can be broken down into three 
sub-processes, inner orientation, relative orientation and absolute 
orientation. While some organizations will have data on all three sub 
processes others will only have data on the aggregated orientation 
rate. The model is therefore being designed to be capable of dealing 
with both cases and with other similar recombinations. In this way it 
will be possible to utilize the maximum amount of statistical data from 
widely differing organizations. 
At the same time as the main functional production processes and sub 
processes are being determined, the factors which influence production 
rates are identified. It is then possible to create a relation matrix 
linking the influencing factors with the production processes (Jerie, 
1976). 
(*) Prof. Jerie was acting Rector at the ITC during this period