Direct countour line measurements are supported by superimposition,
because overlapping lines can be.avoided.and the edge matching can
be done as mentioned above. For DEM measurements it is useful to show
distribution of measured height information, structure lines and
points for deciding about already sufficient input information for
DEM interpolation. Especially the DEM measurement program PROSA
(Progressive Sampling) is supported by VIDEOMAP /1/. Superimposition
makes guidance by PROSA transparent to the operator.
For orientations superimposing parallaxe point distribution and
measured ground control points is quite helpful. In addition to
orientation tie points for model connections can be visualized to
support aerial triangulations. Other applications could be served
as well, for example within the scope of cadastre by displaying
points such as land marks of property lines.
3.2 Superimposition and data revision
Data required by measurements with superimposition is already mostly
clean. However, revision of data from "blind" workstations is still
necessary. Therefore it could be useful to transfer all data from
several "blind" stations to a single "quality control station" for
checking, correcting and completing.
With digital technology the problem of integrating existing analog maps
is getting up. This is why Zeiss has expanded the PLANIMAP system with
the DIGI-AS program for 2-dimensional digitization /3/. Superimposition
of the current map condition as digitized with DIGI-AS helps to check
converted maps.
Superimposition can be used by the contractor to prove the result
delivered by the supplier.
Most important for map revision is change detection by direct visual
comparison of the "new" stereo model with the "old" digital map. As
all changes are immediately eye-catching, the digital map can easily
be updated according to the new situation. Other tasks with the aim
to compare old with new can be performed. Change of land use might be
detected, for example spreading town planning besides decreasing forests
or alteration of surface soil use. Change of coastal lines or river
deltas might be analyzed for prediction and for taking suitable action.
Check and change detection is also useful for height measurements.
Optical superimposition of the contour lines with the stereo model
enables the operator to prove these data with respect to completeness,
correctness and to the fidelity of the terrain representation.
Displaying grid points with computed height values allows sample
control measurements.
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