uisition 
1 infor- 
graphic 
ise of a 
ic data 
to 3D 
nagine 
virtual 
le con- 
tion of 
üistoric 
tute of 
tre de 
AS) of 
de flat 
apable 
possi- 
one or 
How- 
/s pos- 
ith the 
ave to 
of the 
idvan- 
ich is 
photos 
ering. 
these 
  
Kölbl, Otto 
2.1.1 Visualisation of raster data. The easiest task when using raster data is their monitoring. In order to point out 
some features on maps or plans or for modelling one uses with great advantage vivid presentations which can be moni- 
tored permanently or selectively. The image can be digitised on a simple office scanner and can then be presented as a 
simple image matrix. A permanent monitoring rises however quickly problems as they require considerable place in a 
map. Much more efficient is it if special reference points or even better links are placed in the geometric presentation by 
which these images can be called when needed. The CAD software MicroStation disposes on the so-called ‘Engineering 
Link’ which establishes the reference to raster data but also to more extended descriptions in the form of html-files. 
This link goes even beyond these possibilities and allows also to refer on data over the Internet. In this way we get very 
interesting possibilities concerning the opening of an information system to other resources. 
2.1.2 Integration of orthophotos for visualisation and data acquisition. An important standard for geographic 
information systems is today the monitoring of digital orthophotos together with the vector information of the system. 
Most information systems offer today this possibility. The combination is on the one hand important in order to com- 
plement vector information. On the other hand, we realise that the information content of the map can be heavily 
reduced when using orthophotos without reducing the readability. Furthermore, the orthophoto gives to ordinary people 
the feeling of reliability in the map data and makes it easier to understand a project. 
It is understood that orthophotos also allow the data acquisition. Many objects can be directly digitised from orthopho- 
tos. However, there rise quickly limits in visualisation and it is understood that stereo plotters have much higher per- 
formance as for the optics and the measuring accuracy. The stereo impression is of special importance in this context, 
especially when doing 3D modelling. 
3. WORKING PROCEDURES OF VIRTUAL REALITY 
Virtual reality has many aspects and most people might be familiar with this product in conjunction with film industry 
and video games. However, it is evident that planning and the protection of the landscape have other requirements than 
the entertainment industry. One needs a certain adaptation in order to find the monster of the film industry acceptable. 
However, if one wants to sell a project it must appear attractive and as realistic as possible. The simplest way to obtain 
this objective is to integrate photographic images of the region into the project. In an analogue way one can also pro- 
ceed with video images. In this way very effectful film sequences or images might result, however the way of the cam- 
era must be predefined. Another possibility is a complete reconstruction of the environment with all its buildings and 
the generation of rendering. Then, of course, the way of the observer can be chosen freely and ‘fly throughs’ can be 
generated . 
3.1 Rendering and the introduction of texture 
In order to present an object with the means of computer graphics, it is in general subdivided by finite elements which 
are then coloured (cf. fig. 1). This procedure is limited by the relatively important effort for object measurements and 
the subsequent object presentation. For the rendering of the surface elements it is an advantage if one does not use 
homogenous colours for the surfaces but one integrates also the texture which represent the surface as close to reality as 
possible. The next step after texturing is the consideration of the illumination. The easiest way is to choose the bright- 
ness of the surface as a function of the incident light. If one uses several light sources or a diffuse ambient light there 
results already quite favourable effects. Furthermore, one should take into consideration that also neighbouring objects 
influence the light energy and contribute to the brightness of a surface. In order to get even closer to reality one should 
also take into consideration the effect of the reflection of the different objects and finally distance object should be 
covered by a certain distance fog. All this effect should also be taken into consideration. All these effects change not 
only the surface as a whole of an object but should also be taken into consideration as for the texture. Although the 
computer capacity is constantly increasing one obtains soon limits as for a realistic object reconstruction. 
3.2 Draping and pasting of static images 
In order to reduce the effort for modelling there are several possibilities in incorporating images and photographs. First 
of all synthetic model objects can be combined very effectfully with images. There are however limits when the angle 
of view has to be changed considerably. The next step is to drape this image on a simple object modelling. It is very 
effectful to drape orthophotos over a digital terrain model and the angle of view can be largely varied. Certain software 
products like Perspective Scene of Helava allows to introduce artificial 3D objects into the landscape in order to give 
also buildings a more or less realistic appearance. Even more effectful is it to use additional terrestrial photographs of 
the facades of houses in order to project these images onto the geometrically reconstructed objects. 
  
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B5. Amsterdam 2000. 447