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The Federal Office of Metrology and Surveying
(Bundesamt für Eich- und Vermessungswesen) in Austria
is doing data compilation by means of photogrammetry.
They started in 1976 on analog stereo plotters by
measuring profiles in aerial images with scale 1:30000.
About ten years later the method changed to compiling
profiles, breaklines, formlines and spot heights on
analytical instruments from image material with scale
1:15000. The complete data set consists of about 80
millions of points.
Figure 1: DTM from Austria (250 m x 250 m grid)
(Data: Institute for Photogrammetry and Remote Sensing, TU Vienna)
In Switzerland the Federal Office for Topography
(Bundesamt für Landestopographie) uses a completely
different approach. Topographic maps with scale
1:25000 are scanned and contourlines, lakes and spot
height points are extracted semi-automatically.
Figure 2: DTM of Switzerland (250 m x 250 m grid)
(Data: RIMINI Model, Federal Office for Topography)
The situation at the Bavarian Office for Surveying
(Bayerisches Landesvermessungsamt) is very similar to
Austria. An essential difference is, that they are involving
private companies for data compilation.
Practically any method (manual digitizing of contour
maps, tacheometric surveys, ...) can be used, which can
deliver data economically, as long as the results are 3-
dimensional and accuracy demands are fulfilled.
3. CODING AND STRUCTURING OF TOPOGRAPHIC
DATA
Topographic data are organized either as line objects
(ridge, dam, river, ...) single objects (spot heights, ...) or
groups of point objects (photogrammetrically compiled
grid data, ...). The meaning of an object is described by
assigning feature code information to it.
In practice two different approaches can be selected. One
way is to code the data depending on geomorphological
criteria (breakline, spot height, ...) or on how to influence
different interpolation methods when calculating DTMs,
while the other method is to assign really the actual
meaning of the object (brook, dam, slope, ...). In
consideration of long-term administration and usage of
161
the data, it is most desirable to keep as much coding
information as possible.
4. APPLICATION OF TOPOGRAPHIC DATA
Of course topographic data are used to manage internal
projects of surveying authorities or to work on behalf of
other institutions. But an increasing demand emerges
from private customers too. As long as the data are used
only for internal purposes, it is rather easy to adapt data
organization to a few typical production processes. Much
more requirements have to be satisfied when executing
requests from customers because of the variety of DTM
products, data exchange formats and also because of
strict deadlines. To enable efficient project management,
all the necessary technical resources must be applicable
in a highly flexible manner.
5. SOFTWARE SOLUTION
Based on these previously sketched general remarks and
topics a concept for a software package (SCOP.TDM)
has been designed and finally implemented at the
Institute for Photogrammetry and Remote Sensing at the
Vienna University of Technology. Although this paper
deals mainly with managing country-wide topographic
data, most parts of it are applicable for private surveying
companies too. In this case more the inhomogeneity of
the data is of importance than the huge amount data.
5.1 Strategy
The concept follows two main goals. Naturally most
important is an efficient long-term storage and archiving
of topographic data. This not only concerns geometry
(coordinates) and coding, but also information about
other data characteristics (accuracy, compilation method,
authorized data users, ...), because these additional
properties allow for good individual data selection. On the
other hand it is necessary to provide a qualified basis for
DTM application programs. Frequency of data access
during operating on an actual project is much higher than
access to an archive. This in any case enforces to store
the topographic data permanently on the computers hard
disk during work on a DTM project. But for archiving
purposes also removable external direct access media
should be considered as an acceptable alternative. In
some situations there may be no clear distinction
between project and archive phase when most parts of
the data are used nearly all the time. So it should be the
users decision to choose proper data organization.
Finally another important topic is compatibility with other
DTM packages by flexibly supporting different data
formats for data import and export.
5.2 Data Base Manipulation System
A data base manipulation system (TOPDB) has been
completely developed at the Institute for Photogrammetry
and Remote Sensing at the Vienna University of
Technology to store, manage and archive topographic
data (Loitsch, Molnar, 1991). It is a relational data base
system, that has been extended by geometric/topological
elements and appropriate — geometric/topological
operators to handle these elements.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B2. Vienna 1996