Oberkochen, for instance, has developed an automatic (electronic)
Contourliner which may replace the dropped line attachment of the Ortho-
projector when the latter is used in the off-line mode (Ref.: Hobbie
1971). Contrary to the dropped line device, where only the intersections
of each profile with the contour levels are recorded, the Contourliner
makes use of all profile heights - the profiles being scribed in
analogue form on glass-plates as follows. At steps of 0.1 mm in the
direction of the profiling (X-direction), the two points situated on
neighboring profiles and having the same Y-coordinate, are connected
in space by a straight line. This Straight line is then intersected
by a horizontal plane representing a contour level and the point of
intersection is vertically projected (actually photographed) onto the
contour chart, as a contour point. Using this device, the time needed
to prepare finalized contours may be reduced significantly, but the ac-
curacy of these contours will not be greatly improved because the
errors in the contours still depend largely on the errors in the pro-
filing and still lack the information in between the profiles.
Another system, al
realized ii more digital way, is proposed, or under experiment, at
several places (Powell 1971, Ducher 1971, Dubuisson 1971, Szangolies
1971). This system is as follows: during the profiling, the profile
data (x.y,z,) are to be recorded on magnetic tape. This tape is to be
fed to a computer which - preferably after some smoothing of the pro-
files - shall carry out the interpolation computations that lead to the
determination of the planimetric coordinates of the contour lines.
These coordinates shall then be fed to an automatic drawing table in
the required format.
ong the same line and leading to a similar result but
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Finally, your attention is called to two very interesting systems, in
each of which, the phase of orthophoto production is separated from
the phase of preducing the height information but where nevertheless
one phase depends on the other, to the benefit of thé system.
The principles of these two systems, however, differ very much and also
their products have quite different characteristics.
The first system is the one originally conceived and developed by
Drobyshev (Ref.: Drobyshev 1968, Visser 1969) and discussed in a broader
sense by Makarovic (Makarovic 1971). Putting much emphasis on the need
for optimum accuracy and completeness of the height information, Dro-
byshev advocates convential (manual) contouring of the stereo-model
(first phase). Having the contour plot available, the heights of the
profiles which shall be followed by the floating mark (and slit) in the
subsequent traversing for orthophotograph production are known (ie,
can be derived from the contour plot). In principle the relevant data
for each profile may be stored on tape or punched cards and subsequently
be fed to the differential rectifier for fully automatic production of
the orthophotograph (second phase). The actual problem concerns the
derivation of the profile heights from the contour plot (intermediate
phase). Drobyshev describes a method which is largely manual and thus
time-consuming. It is clear that, here too, automation is possible.
5
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