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CONTRIBUTION TO THE DTMs STUDY 
(DTM ON DRAINAGE STUDIES) 
Patmios E., Professor 
Laboratory of Photogrammetry-Remote Sensing 
Dept. of Civil Engineers 
Polytechnic School 
Aristotle University of Thessaloniki GREECE 
Commission IV 
ABSTRACT 
In this paper the subject of DTM is dealt with, on the base of a triangle net of sampling points. 
The basic principles of digital model are presented as well some products (indicatively contours, secti- 
ons, etc.). 
The example concerns an area of Athos peninsula, which is especially important as historic (monastic) 
center. 
The digital model was chosen at first as suitable for the mountaineous relief, but it can also be used 
for general applications. 
Many cartographic facilitations can be achieved based on this DTM. 
Furthermore, requirements of geoinformation systems and aspects of correlation with sattellite data can 
be facilitated. 
1. INTRODUCTION 
Several internal and external factors in combina- 
tion with human action, have formed and continue 
to form the shape of the surface of the earth. 
Sciences as geomorphology, geology, geodesy, pho- 
togrammetry, Remote Sensing etc, study among othe- 
rs the surface and generally the crust of the 
earth from various aspects. The study concerns the 
qualitative and quantitative research in correla- 
tion, or not, with the relevant dynamic causes. 
In this research the presentation of the forms 
oontinues to be the basic pursuit. Several methods 
have relatively developed at times, with advanta- 
ges and disadvantages correspondingly. The con- 
tour curves constitute a specially useful way of 
presentation, with which the scientists and te- 
chnologists are particularly familiar. Scientific 
and technological progress, automatisms etc., 
contineously improve the considerations about the 
methods of presentation of landforms. 
On this base the considerations on DTM present 
particular advantages and for this reason their 
study has multiple interest, theoritical and pra- 
ctical, not only for the presentation of the 
landform but for every other form (architectural 
elements, etc.). 
For a totality of points for which we know with 
some method (topographic, photogrammetric etc.) 
the altitude (sampling points), the mathematical 
Structure and the calculation procedure for find- 
ing, basing on the above, the altitude of other 
point in the consideration area, in generally the 
content of a DTM (4). 
For all the cases, except the others, the choice 
of the sampling points is basic stage, determinal 
for the quality of all the work. The sampling 
points may form nets of various kinds (orthogonal, 
Square, triangular etc.) regular or irregular. 
They also may be taken along different lines (co- 
ntours, morphological etc.) or at various combi- 
nations of the above with the correspondent ad- 
vantages and disadvantages. The choice of the 
sampling points may be determined from the begin- 
ning or during the measurements. Method of the 
sampling procedure which allows the progressive in- 
crease of the density of sampling points, based on 
some criteria, where the landform demands (1) or 
compound works of additional taking of lonely and 
characteristic sampling points (2), especially 
surve the whole problem of DTM. The method of 
sampling that is being used, in combination with 
the landform (categories of terrain) constitute 
determinal factors for the general quality of all 
the works, as accuracy benefit, etc. 
The above concern only some characteristic points 
from the research relatively to DTMs. Therefore it 
is obvious that the general study of DTMs is a 
multiple and compound work which continues to be 
systematically faced (isolated researchers, Insti- 
tutes, work groups of International Commissions 
eto. 
At some cases it is useful and realistic local par- 
ticularities and factors to be seriously taken up 
in mind (weakness in substructure of DTMs, various 
necessities in applications, general developing 
plans, particularities of the relief etc.). 
Of this point of view, and to continue our previous 
study (3), we developed a DTM basing on a triangu- 
lar net of sampling points. 
The basic principles of the mathematical model, of 
the sampling procedure and the calculation of sec- 
tions and contour curves are shortly presented in 
this paper. An example for the case of study of a 
drainage net is also presented (area of Agio Oros, 
Athos Peninsula, Greece). 
2. BASIC PRICIPLES OF THE DTM 
At the presented DTM the surface of the land is at- 
tached by a polyhedral surface which has triangles 
as faces, with apexes the sampling points. 
Basing on this surface, for every other point P 
with horizontal coordinates Xp, Yo; which belongs 
in the limits of the surface determined by the sa- 
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