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A5, —
By far the most complicated task is the establishment of accuracy models for the
determination of minor control. The reasons for this are the large number of
influencing factors and possible combinations between various preparation —
observation and adjustment methods, and the influence of the large number of
possible configurations and flight patterns of the photographic coverage.
Therefore accuracy models should be established, considering only the most
important process parameters as variables and considering other factors
(especially those pertaining to the executing organisations) by applying
calibration factors, which can be assumed to be more or less constant for an
individual organisation.
Three different methods can be used for the establishment of accuracy models:
a) Analysis of practical experiments.
b) Theoretical analysis using functional and stochastic models of the actual
‘physical process
c) Application of computer simulation
To the author's opinion the last method in conjunction with carefully designed
practical experiments offers the best results as more realistic assumptions concern-
ing the error sources and their stochastic properties can be applied as in method
by.
21, Establishment of semantic information models
This information is required by the planner in order to make sure that the semantic
information (i.e. the types and kinds of natural and cultural features) required
by the product specification can be achieved.
In the first place this will depend on whether these natural and cultural features
can be identified and classified on the aerial photography with sufficient
reliability. This is primarily a function of the photoscale, the type of camera
and film-filter combination used and the photographic processing.
Furthermore we have to consider the loss of information due to the various
processes applied, the optical properties of equipment used, the Skill of inter-
preters etc.
Alternative means for the planner to achieve the necessary semantic information
include the application of premarking (signalisation), field identification
carried out before plotting and field completion. Therefore, from the economic
standpoint there exists a very strong trade-off position between on the one hand
the choice of photoscale and the cost of resulting photogrammetric work and
-