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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.