projects in future. Therefore, MapSof/DGM data are 
structured in a manner which ensures their full utilization 
by GIS. The main concern of MapSoft is to secure the 
quality of the acquired data in terms of completeness 
and accuracy, which can be realised through adequate 
functions for data acquisition, primary analysis and 
processing. The optimum solution for achieving this 
goal, which has been applied within MapSoft, is 
interactive verification of data during the acquisition 
stage. Of course, it is understood that procedures for 
making these data official, and their constant updating 
are equaliy important. The same principles were used in 
realization of the module for the DTM support. 
3. THE SOFTWARE CONCEPTION 
There are several requirements that were imposed to the 
software: 
e For efficient and high quality digital terrain 
modelling, it is essential to enable measurement 
and processing of all kind of the DTM data. This 
includes selective, systematic and progressive 
sampled data as well as the data from contour 
digitization. Height information such as structure 
and break lines and flat areas have to be fully 
respected. 
e |nteractive and efficient data measurement, 
verification and editing are required. Functions for 
visual and rigorous analytical checks of the 
acquired data must be provided. This should be 
based on analysis of the DTM created from the 
acquired data. 
e The software must follow the basic conception of 
the MapSoft in order to be fully integrated with 
other modules. Already developed user interface 
should be used as much us possible to make the 
training easier. 
4. THE SOFTWARE REALISATION 
Standard functions of the MapSoft: data base 
management, functions of the graphical interface, 
measuring device support, plotting and the like were 
used for the development whenever possible. 
The software is implemented through the design of data 
base and through the development of functions for data 
acquisition, DTM creation and DTM analysis and data 
verification. 
4.1 Data base 
The existing MapSoft data base has been extended with 
new spatial entities. The flexible data model includes 
spot heights, characteristic terrain lines, measured 
contours and areas (lakes, the areas under the objects, 
and so on). 
208 
Two optional solutions for extension of MapSoft with the 
DTM module have been considered. Each of them 
assumes that the existing MapSoft's data base has to 
be extended with spatially and topologically organised 
DTM data. 
The first solution, which is currently implemented, 
assumes that only basic topology necessary for 
handling DTM data is stored and updated within 
MapSoft’s data base. TIN based DTM is generated only 
for selected part of the project area at the moment when 
the analysis of that area is required. This simplifies and 
speeds up functions for data input and update. This is 
useful during data acquisition stage when a large 
amount of data is to be processed within on-line 
measurements. However, after data editing or after the 
new measurements have been done, the DTM has to be 
generated again. This has to be done every time the 
verification of the acquired data is to be made. When the 
data acquisition and verification are completed, the final 
DTM can be generated for the whole project area. 
The second solution assumes on line generation and 
constant upding of full DTM topology for the whole 
project during data acquisition stage. After several 
measurements, updating of TIN topology and surface 
calculation are performed. The updated DTM data base 
can be used for further analysis right after. All in all, this 
solution is more efficient then the first one but it requires 
additional functions for updating of the DTM topology 
after each data editing. Otherwise, it should not be a 
problem to implement this algorithm. Due to the design 
of DTM data base these functions for DTM editing will be 
easily developed. It is important that the same functions 
for TIN surface generation are used in both solutions so 
the final results are the same. 
4.2. Data acquisition 
Using the existing MapSoft interfaces to digitization 
devices, the following data acquisition methods are 
supported: 
e photogrammetric measurement 
e on-screen manual digitization of the scanned maps 
e digitization of maps on digitizing tablet. 
The same principles apply to all three methods of data 
acquisition. The only difference is that in case of the 
second and third methods, heights for points and 
contours have to be entered manually from the 
keyboard. In this paper photogrammetric techniques will 
be considered. 
All known strategies for the DTM data acquisition are 
supported. Of course, some modifications were 
necessary due to the limitations imposed by use of 
analogue instruments. This means that in case of 
systematic or progressive sampling, operator has to 
manually drive measuring mark to the marked positions 
that are chosen by computer for measurement. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996 
198 
cre 
sid 
lim 
me 
dei 
Co 
crit 
dut 
tim 
crit 
Sta 
anc 
attr 
line 
the 
WO! 
cor 
USE 
bas 
4.3 
Irre 
infc 
ane 
ma 
TIN 
chc 
pro 
Tri 
ger 
whi 
dev 
alg: 
(Re 
Del 
con 
ach 
brie