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that updating of existing cartographic data bases is much more
time consuming than an initial production of a GIS base related
to geometrically correct sources. By the use of satellite images
as background information it is possible to reduce the number
of interpreted features, which allows a reduced time schedule
compared to traditional mapping while maintaining quality,
without any significant reduction of the interpretability of the
final map product.
Database. Experiences from these three Baltic data base and
mapping projects amplify the impressions from earlier data base
establishment projects. Data bases generally include
information stored from digitized maps, based on
cartographically handled information. Today this information is
not accurate enough when combining the cartographic data with
geographically correctly positioned information in a GIS
environment.
Homogeneous data base quality is of greatest importance for
future data usage in combination with external sources. The
quality of the data from the Base Map projects allows a
combined use with external data sets for production of among
other things thematic maps. In other words, the information
stored in the data base, with its well-defined geometry and
coding, constitutes a platform for further data and map projects.
Map design. When evaluating the map design of the three
Baltic projects, the main technical purpose which is the
establishment of a flexible data base, has to be taken into
account. The reduced time schedule, which results in a map
product containing an image background as complementary
information to interpreted and coded features, has an effect on
the cartographic balance and layout. Topographic maps in
general do not include image backgrounds, which resulted in
the need for investigation and development of production
procedures optimizing the use of satellite data in combination
with traditional feature information.
Education. The development of personal skills using remote
sensing products in a digital environment, is an aspect that
should not be overlooked, during such big projects. In
combination with the development of interpretation and GIS
procedures such projects include the whole spectrum of the
latest techniques in map production.
Time schedule. Due to the minimized production time of these
projects it was necessary to optimize the production procedures
with remained expenses. This resulted in the following
possibilities and decisions:
* Initial training including remote sensing, interpretation
technique and GIS.
* Satellite Ortho Photo Maps as main sources during the
interpretation.
* The number of GPS measurements as ground truths was
minimized by the usage of SSC Satellitbild's orbital
adjustment model.
* Efficient usage of existing information, i.e. contour lines.
* Data Base structure in accordance with the Swedish KF85
nomenclature.
* Lowered ambition of interpreted features, compensated by
an image background.
* Analog interpretation, instead of time consuming screen
interpretation and digitalization.
* Digital cartography, using coded vector data as input to the
map design environment.
* Digital data delivery via the Internet.
4. CONCLUSIONS
Position accuracy in orthophotos, geometrically corrected by
GPS measured GCP:s and a generalized DTM, based on
panchromatic SPOT data on a scale of 1:50,000 in combination
With multispectral data on a scale of 1:100,000 are feasible
information for revision of topographic maps on a scale of
1:50,000.
459
The homogeneous data base quality, high geometrical accuracy
and "intelligent" coding, allows effective data extraction and
further combination with external data sources.
A balanced cartographic product, combining satellite images
and interpreted features from different sources, without any
decreased quality, verifies the value of topographic base
mapping projects.
A combination of initial education (remote sensing,
interpretation and GIS) followed by production is an efficient
method for technical transfer during mapping projects similar to
the Base Mapping Projects in the Baltic States.
By using a digital technique, methods performing semi-
automatic revision of existing data bases, it will be possible to
increase the position accuracy and also reduce the time
consuming part, manual interpretation, of data base revision
projects in the future.
5. REFERENCES
CNES and SPOT Image, 1988. SPOT user's handbook.
Dahlgren A., Svedjesten L., 1993. Control Point Determination
with GPS for Precision Correction of SPOT Satellite Images.
Master of Science Thesis. The Royal Institute of Technology,
Department of Photogrammetry, Stockholm, Sweden.
Harris R., 1987. Satellite Remote Sensing - An Introduction,
Routledge & Kegan Paul.
Krusberg P., 1994, Estonian Base Map Project, Estonian Map
Center.
Malmstrôm B., Engberg A., 1991. Satellitedata for Topographic
Mapping, Swedish National Land Board, Swedish Space
Corporation. (Swedish)
Rosenholm D., 1987. Some Aspects of Least Squares Matching
for Automatic Parallax Measurements. The Royal Institute of
Technology, Department of Photogrammetry, Stockholm,
Sweden.
Westin T., 1991. On the Estimation of Interior and Exterior of
SPOT Imagery. The Royal Institute of Technology, Department
of Photogrammetry, Stockholm, Sweden.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996
