projects in future. Therefore, MapSof/DGM data are
structured in a manner which ensures their full utilization
by GIS. The main concern of MapSoft is to secure the
quality of the acquired data in terms of completeness
and accuracy, which can be realised through adequate
functions for data acquisition, primary analysis and
processing. The optimum solution for achieving this
goal, which has been applied within MapSoft, is
interactive verification of data during the acquisition
stage. Of course, it is understood that procedures for
making these data official, and their constant updating
are equaliy important. The same principles were used in
realization of the module for the DTM support.
3. THE SOFTWARE CONCEPTION
There are several requirements that were imposed to the
software:
e For efficient and high quality digital terrain
modelling, it is essential to enable measurement
and processing of all kind of the DTM data. This
includes selective, systematic and progressive
sampled data as well as the data from contour
digitization. Height information such as structure
and break lines and flat areas have to be fully
respected.
e |nteractive and efficient data measurement,
verification and editing are required. Functions for
visual and rigorous analytical checks of the
acquired data must be provided. This should be
based on analysis of the DTM created from the
acquired data.
e The software must follow the basic conception of
the MapSoft in order to be fully integrated with
other modules. Already developed user interface
should be used as much us possible to make the
training easier.
4. THE SOFTWARE REALISATION
Standard functions of the MapSoft: data base
management, functions of the graphical interface,
measuring device support, plotting and the like were
used for the development whenever possible.
The software is implemented through the design of data
base and through the development of functions for data
acquisition, DTM creation and DTM analysis and data
verification.
4.1 Data base
The existing MapSoft data base has been extended with
new spatial entities. The flexible data model includes
spot heights, characteristic terrain lines, measured
contours and areas (lakes, the areas under the objects,
and so on).
208
Two optional solutions for extension of MapSoft with the
DTM module have been considered. Each of them
assumes that the existing MapSoft's data base has to
be extended with spatially and topologically organised
DTM data.
The first solution, which is currently implemented,
assumes that only basic topology necessary for
handling DTM data is stored and updated within
MapSoft’s data base. TIN based DTM is generated only
for selected part of the project area at the moment when
the analysis of that area is required. This simplifies and
speeds up functions for data input and update. This is
useful during data acquisition stage when a large
amount of data is to be processed within on-line
measurements. However, after data editing or after the
new measurements have been done, the DTM has to be
generated again. This has to be done every time the
verification of the acquired data is to be made. When the
data acquisition and verification are completed, the final
DTM can be generated for the whole project area.
The second solution assumes on line generation and
constant upding of full DTM topology for the whole
project during data acquisition stage. After several
measurements, updating of TIN topology and surface
calculation are performed. The updated DTM data base
can be used for further analysis right after. All in all, this
solution is more efficient then the first one but it requires
additional functions for updating of the DTM topology
after each data editing. Otherwise, it should not be a
problem to implement this algorithm. Due to the design
of DTM data base these functions for DTM editing will be
easily developed. It is important that the same functions
for TIN surface generation are used in both solutions so
the final results are the same.
4.2. Data acquisition
Using the existing MapSoft interfaces to digitization
devices, the following data acquisition methods are
supported:
e photogrammetric measurement
e on-screen manual digitization of the scanned maps
e digitization of maps on digitizing tablet.
The same principles apply to all three methods of data
acquisition. The only difference is that in case of the
second and third methods, heights for points and
contours have to be entered manually from the
keyboard. In this paper photogrammetric techniques will
be considered.
All known strategies for the DTM data acquisition are
supported. Of course, some modifications were
necessary due to the limitations imposed by use of
analogue instruments. This means that in case of
systematic or progressive sampling, operator has to
manually drive measuring mark to the marked positions
that are chosen by computer for measurement.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996
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