ectronic)
nt of the Ortho-
(Ref.: Hobbie
the intersections
e Contourliner
ribed in
‚1 mm in the
situated on
re connected
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he point of
red) onto the
1e time needed
ly, but the ac-
cause the
5 in the pro-
Files.
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eriment, at
, Szangolies
, the profile
tape is to be
| of the pro-
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ur lines.
ng table in
| Systems, in
ated from
evertheless
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much and also
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ed in a broader
is on the need
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ereo-model
ights of the
d:slit) in the
known (i.e.,
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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.
wl