Full text: International cooperation and technology transfer

triangular irregular network (triangulation 
including all measured points - breaklines and 
formlines are maintained in the stored data, full 
3D is possible, much greater data amount as for 
regular grids) 
hybrid structure (regular grid with additional 
information about breaklines and formlines, also 
combination with TIN areas is possible) [Kraus 
K., Jansa J., Kager H., 1997] 
The quality of the computed orthophotos also 
depends a lot on the used DTM. Concerning 
orthophotos for small scale (pixelsizes greater than 
10 m) a regular grided DTM will be sufficent to 
obtain good results. For large and medium scale 
orthophotos the used DTM should also consist of 
additional structure information. If orthophotos with 
pixelsizes of 1 m or less have to be generated also 
buildings must be taken into account. 
Digital terrain models and orthophotos are widely 
used and a lot of products can be derived from them 
(isolines, profiles, perspective views, intersection 
with other data, volume calculations). Such results 
are used either as the basic information for further 
analysis or as final plots for visualization and 
presentation (Figure 1). 
Figure 1 DTM representation of isolines, breaklines, 
formlines and outlines of buildings. 
Depending on the object information and level of 
complexity there are different levels of visualization 
for the derived products mentioned above (wire 
frame, shading, texture mapping, integration of other 
data such as roads, buildings or thematics). All 
these outputs can be produced with high quality and 
accuracy and therefore are suitable for a lot of 
A disadvantage of these outputs is the lack of 
flexibility. A shaded and texture mapped perspective 
view of a DTM is a very illustrative tool for giving a 
more realistic appearance to landscape and larger 
areas, but it is still a static view of a much more 
complex model. To show the complexity, a lot of 
different plots from different points of view have to 
be created. 
In some cases, especially when discussing with 
customers and sponsors, it is of the same 
importance to present results in an appropriate and 
more impressive way. Imagine your customer can 
move over the DTM and explore and analyze the 
model in real time! As in today's world everything is 
rotating and moving it seems obvious to look for a 
possibility to perform interactive, dynamic, real time 
DTM visualization and animation. 
The problems that arise are not issues of basic 
algorithms (computer graphics has reached a high 
level of sophistication), they are rather problems of 
handling very large data sets under time- 
constrained conditions. Some of the requirements 
for efficient visualization are distributed worlds, 
levels of detail and image compression. 
"Distributed worlds" means that the whole DTM is 
divided into different parts, each one representing 
an own smaller DTM. So, only the visible parts 
(determined by using a viewing pyramid) need to be 
loaded. Using this concept, the amount of data to be 
hold in memory at the same time can be reduced by 
approximately 75 percent on average. 
A further increase of performance can be achieved 
by utilisation of levels of detail (LOD). "LOD is a 
mechanism used in computer graphics to improve 
the drawing speed of complex scenes [Clark J.H., 
1976]. Each object is stored several times in 
different levels of quality (levels of detail). During 
visualization each object is drawn in the optimal 
level of detail. The chosen level depends on the size 
of the object in the current view. Objects that appear 
small can be drawn in little detail (and therefore very 
fast) without loosing quality; in contrast, objects near 
the point of view that cover a lot of space on the 
screen need to be rendered in full quality." [Kofler 
M., Rehatschek H., Gruber M., 1996]. Although the 
total amount of data is increased by storing different 
LOD in a pyramid structure, the current memory 
demand during interactive visualization can again be 
reduced dramatically. 
As a last way of data reduction, image compression 
should be mentioned here. When visualizing a DTM

Note to user

Dear user,

In response to current developments in the web technology used by the Goobi viewer, the software no longer supports your browser.

Please use one of the following browsers to display this page correctly.

Thank you.