ectronic) 
nt of the Ortho- 
(Ref.: Hobbie 
the intersections 
e Contourliner 
ribed in 
‚1 mm in the 
situated on 
re connected 
intersected 
he point of 
red) onto the 
1e time needed 
ly, but the ac- 
cause the 
5 in the pro- 
Files. 
[lar result but 
eriment, at 
, Szangolies 
, the profile 
tape is to be 
| of the pro- 
iat lead to the 
ur lines. 
ng table in 
| Systems, in 
ated from 
evertheless 
tem. 
much and also 
loped by 
ed in a broader 
is on the need 
mation, Dro- 
ereo-model 
ights of the 
d:slit) in the 
known (i.e., 
relevant data 
nd subsequently 
production of 
oncerns the 
intermediate 
nual and thus 
S possible. 
Metricál information of the terrain relief can be conyerted by an elec- 
tronic digital computer into signals suitable for the control of the 
automatic orthophoto printing. Signals are needed to provide correc- 
tions for relief- (and tilt-). displacements, so that the resulting 
orthophoto is at least differentially scaled. If the orthophoto printer 
is equipped with the appropriate correction devices further signals may 
be derived from the contour-plot to correct the projection for the 
distortions caused by the terrain slopes, or even terrain curvatures 
(as well as signals from the tilt information to correct the projection 
for the effect of negative tilt). ! 
"For automatic orthophoto-printing, different equipment and techniques 
are applicable. The equipment may range between simple direct optical 
projection printers and sophisticated optical-electronic printers." 
(Makarovic 1971). 
The second system is based on the conception of Collins (Ref.: Collins 
1968), called the Stereo-Orthophoto, developed by the National Research 
Council of Canada (Blachut and van Wijk-1970, Schut-1971) +" Details of 
the Stereo-Orthophoto system will be given later in this presentation 
by Mr. van Wijk. 
NRC emphasizes (Blachut 1971) that "once the stereo-orthophotos are 
obtained, there is no need - and it is often wrong - to use the original 
aerial photographs to extract any further data needed for the production 
of an orthophoto map. This can be accomplished. much more efficiently 
and at significantly less cost from the stereo-orthophoto pairs." One 
should, however, not forget that the orthophotos are deteriorated by 
the orthophoto process: a deterioration of the geometry due to profiling 
errors and finite slit-length (errors in the planimetry of the ortko- 
photograph, y-parallaxes and errors in the x-parallaxes-and: thus in the 
heights - of the stereo-módel, and double images or gaps along the edges 
of the profiles) as well as a deterioration of the image quality (reso- 
lution) of both orthophoto and stereomate. The geometrical errors, 
however, are only small and practically negligible for terrain slopes. 
up to 10 to 15 degrees. Moreover, the effect of the parallax errors 
may be considerably reduced by introducing the artificial x-parallaxes 
into the Stereomate by a wedge with an appropriately curved surface and 
using a corresponding non-linear height-scale instead of a plane wedge 
and a linear height-scale (Ref.: Collins 1969, Blachut and van Wijk 1970). 
The deterioration of the image quality, however, remains. 
The fact that both systems, described above, the "Drobyshev-Makarovic" - 
system and the Stereo-Orthophoto system, are broken down into phases 
that may be carried out separately in time and location may also be 
attractive from an organizational point of view. 
Experimental Results From the Stereo-Orthophoto Technique 
One of the systems of developing height information from orthophotographs 
mentioned by Mr. Visser was the stereo-orthophoto technique. . A descrip- 
tion of the equipment, the techniques used and some results obtained in 
large scale mapping experiments are given. 
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