qualified. Storage of profiles enables an improved model approxi- 
mation by ''electrical interpolation' of intermediate profiles. 
Projection may be performed in smaller scanning paths without any 
additional work for the operator. ‘''Optical interpolation (0-Int)" 
by inclining of the projection surface up to + 35° is possible in 
order to reduce the system errors. 
Figure 1 shows the effect of decreasing the scan width in the 
° QO» . . ° 
representation of a h5" inclined ledge. |t is obvious that the 
system errors must be diminished as far as possible in order to 
preserve the original shape of the object. An improvement of 
the model approximation by electronic scanning systems and digital 
guiding of orthoprojectors is anticipated for the future. 
Profiling errors such as displacements between adjoining strips 
appear if the object is inclined in the scanning direction or if 
the curvature of the surface changes suddenly, which is shown in 
figure 2 for the border of a cupola. The only way to minimize 
this kind of displacement is the reduction of the scanning speed. 
For architectural orthophoto work a variable profiling speed 
should be possible in any case. Moreover the Y-drive should be 
stoppable during the scanning procedure in order to follow pro- 
truding parts of the object with the floatina mark. This possi- 
bility is only available in a few orthoprojection systems. 
2.3. Subsequent treatment of orthophotos 
The pure orthoprojection is followed by reproduction work for the 
adaptation of scale, for photo-mounting and retouching. Experience 
has shown that several copying processes do not really affect the 
quality of the final product if careful photographic treatment is 
provided. For the preparation of photomaps little retouchina is 
normally necessary. 
If line maps are required by the client they can be derived from 
orthophotos by direct tracing on overlay sheets. This work does 
not need a photogrammetric operator and should be carried out in 
architectural style. Methods of transforming continuous-tone 
photographs to line maps automatically by equidensities, Agfacon- 
tour film or by "''pictoline technique' are in the experimental 
Stage and cannot be considered to be operational. 
A further way of representation seems to be the graphic combination 
of photomaps and linemaps. Thus architectonic elements of impor- 
tance can be restituted by stereoplotting, while painted or de- 
corated surfaces are produced as rectified photographs. Both 
parts can then be joined graphically. Architectural plans are