440 
In the second step, the basic data and tie points are transformed to the 
model space (by the collinearity or another transformation). The process 
is iterative (fig. 9) (Radwan, 1980). Usually three to four iteration 
cycles per point suffice. 
The third transformation step serves for local merging of the changed 
data into the existing data base. Thus the basic data are transformed 
into the coordinate system of the data base, whereby corrections for 
deterministic errors (e.g., shrinkage of map) and cartographic projection 
can be implemented. Usually local affine transformation provides satis 
factory results (Beotra, 1981; Bescenicar, 1976; Radwan, 1980). 
Figures 3 and 4 indicate how the changes are applied to the existing 
data base. 
Fig. 9: Iterative photo- to model transformation. 
OPERATIONAL CHARACTERISTICS 
The operational characteristics concern the system as a whole, each stage 
of the process, the equipment components, human factors, performance and 
reliability, and the compatibility of output. 
The overall system properties concern issues such as versatility and 
flexibility of the DMP system; modular set-up; phased, parallel and de 
centralised operation; balanced work load and time-lined data flows; and 
compatibility of components and of data. Most of these properties are in 
terdependent and are strongly influenced by the system design. 
The main phases of the process, i.e., the preparation, mensuration, trans 
formations, and plotting, are serial and can be time-delayed. Moreover, 
the operations are modular in each phase. Hence, optimisation of each 
phase contributes to the optimisation of the overall process. 
From a human engineering point of view, it is advantageous that in each 
phase the specific skills can be employed. The most delicate phases are 
preparation, mensuration, and pre-editing the changed data. These ope 
rations should be thorough and time-efficient. 
The equipment architecture may be composed of the existing components 
(Makarovifi, 1973), though a simple dedicated instrument for measurements, 
permitting stereoscopic observation is preferable. The xy-digitising from 
a single photograph should be combined with the x-parallax measurement/ 
digitising. Moreover, a simple plotting device should be attached to 
produce a check plot in real-time. Such a device is not needed if a 
graphic display terminal for interactive operation is connected.