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Title
International cooperation and technology transfer
Author
Fras, Mojca Kosmatin

134
DATA INTEGRATION FOR THE DTM PRODUCTION
Tomaz Podobnikar
Dr. Zoran Stancic
Kristof Ostir
Scientific Research Centre of the Slovenian Academy of Sciences and Arts
Gosposka ul. 13
SI-1000 Ljubljana
Slovenia
ISPRS WG VI/3 and IV/3 meeting: Bridging the Gap, Ljubljana 2-5 February 2000
KEY WORD: digital terrain model, digital elevation model, interpolation, SAR interferometry, GIS, quality control
PURPOSE:
In the late 1970’s Surveying and Mapping Authority of the Republic of Slovenia produced digital elevation model
(DEM) with grid size of 100 m. The DEM was intensively used for numerous cartographic, GIS and planning purposes in
the past, but nowadays it does not fulfill demands due to its poor spatial resolution and height accuracy. Therefore
Surveying and Mapping Authority has started activities for better DTM production. After initial stages and some case
studies, the expected quality of the new DTM was not achieved.
The main objective of this paper is to present and discuss the possibility of improving existent DEM of Slovenia. Many
techniques are available to produce high accuracy DEM, but they are not always economical. Our strategy is to model
hydrologicaly and morphologicaly correct DTM (digital terrain model) with high statistical and visual accuracy. We intend
to use different approaches for modeling different physiographic regions of Slovenia. Special emphasis will be made to
the integration of vector contour lines from maps, hydrographic elements and other break lines, automatically derived
relief characteristic points, geodetic points, existing DEM 100, photogrametricaly captured data, SAR DEM, etc.
Results from the case study using this integrated data are very promising. DTM with 25 m grid size for selected regions
in Slovenia with height accuracy of approx. 1 m for predominantly flat and urban areas, approx. 4 m for the hilly areas
and about 10 m for the alpine areas.
1. INTRODUCTION
Spatial databases with adequate quality are essential for
management of modern society demands. Morphology of
relief is one of the most important characteristics of the
natural environment. Digital approximation of its surface -
digital terrain’s surface model - is important for numerous
cartographic, GIS and planning purposes.
The need for a better model resulted in many
experiments, projects and expertises about the strategies
of improvement and needs of new DEM/DTM (digital
elevation model / digital terrain model) in last 10 years.
The results of opinion pool indicated that the most of
potential users would prefer to have DEM with grid
between 10 and 20 m and with height accuracy between 1
and 3 m (Stanonik, 1995).
Few years ago, Surveying and Mapping Authority started
activities for the production DEM with 25 m resolution.
After initial stages and some case studies, the expected
quality of the new DEM was not achieved. Maybe the
main reasons of not satisfying results in DEM / DTM
production in Slovenia are the diametrically opposite
demands: simplification in production methods and
making large - no economical projects for production.
Our approach is to integrate different available height data
sources of Surveying and Mapping Authority, which have
different quality. In last years more and more
georeferenced databases form different sources have
been available. In our case study special emphasis has
been paid to the integration of vector contour lines from
maps, hydrographic elements and other characteristic
lines, automatically derived characteristic lines and points,
geodetic points, DEM 100. We are also performing a
reliable process of quality control of the model.
2. DEFINITION OF THE TERMS DEM / DTM
Definition of DTM / DEM is not an easy task. In the
literature we can find many definitions, from simple to
complex. The reasons of such disorder probably lies in
different techniques of modeling, representation,
recording and fields of interest of relief data applications.
In definition we consider the Earth surface as a
continuous (indiscrete) phenomena, which is attempted to
be represented with function(s). Such functions could be
continuous mathematical or statistical. Digital terrain
model can be understood as “digital description of the
Earth’s surface”. It does not include only representation of
the relief itself but also its description, as slope, aspect,
contour lines, break lines, peaks, and the other
characteristic points. The following components are
needed for complete definition of the DTM (Martinoni and
Bernhard, 1998):
data elements,
.structural information,
continuous functions,
quality information,
methods for implicit functions analyses.
Data elements may be understood as support to the
model. They explicitly describe elevation with points, lines
or areas in the belonging coordinate system. Data
elements are often registered as grid or included in TIN.