Full text: XVIIIth Congress (Part B4)

  
4. PILOT PROJECT 
For studying the applicability of the developed concepts and 
tools, we have first limited ourselves to the modelling of 
buildings, an important component of an urban scene. We 
have built a rudimentary 3D-GIS and report here on the 
components, the data flow and the bottlenecks 
encountered. 
4.1 TREVIS 
The data model presented in figure 1 can be translated into 
different kinds of database structures. The relational and 
object oriented structures are the most interesting ones. For 
practical reasons we have chosen for our proof-of-concept 
demonstrator the relational structure (see figure 4) and 
dBASE IV for es management. 
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Figure 4 Relational data structure of 3D FDS. 
Our experimental 3D vector GIS (TREVIS) is built in a PC 
environment with a Zeiss C120 analytical plotter and a 
Matra Traster T10 digital plotter connected by Ethernet. In- 
house software development was needed for (1) 
reconstructing solid objects from the digitized features and 
structuring the data according to FDS, and (2) interactive 
visualization of 3D objects. For system testing purposes, at 
least, it is necessary to have tools to inspect an object from 
all sides and with different enlargements. Stereoscopically 
presenting objects in perspective wireframe views using the 
anaglyph principle suffices for this purpose. The graphics are 
produced directly from the dBASE files. We can, therefore, 
use this tools to also visualize query results. Moreover, a 3D 
cursor (like a photogrammetric floating mark) allows the user 
to move around in the anaglyph stereomodel and snap to 
the nearest node or to the middle of the nearest arc. The 
obtained node respectively arc identifier can readily be used 
as input to a query. This computer graphics tool can also be 
used for interactive verification and editing of the 
constructed model for applications where only the spatial 
integrity is important and the spatial accuracy relaxed. For 
database updating purposes and demanding accuracy 
requirements, however, sophisticated 3D visualization and 
its superimposition with the photogrammetric model are 
highly desirable. 
We have tested various queries about topologic 
relationships among 3D topographic objects with TREVIS, 
864 
eg, neighbourhood, adjacency and inclusion. The results 
obtained were summarized in (Bric et al, 1994). Here, 
therefore, we shall concentrate on photogrammetric data 
collection, model construction, and visualization. 
4.2 Test ITC 
We had selected two test sites. The first one was an open 
urban area with undulated terrain in Switzerland and a 
photoscale 1:5400. The second area was around the ITC 
building being covered by one stereomodel of 1:2200 scale 
photography. We digitized features of buildings on the Zeiss 
C120 with KORK and on the T10 with DEMETER. Our 
interest, in the pilot study was on finding the best strategy 
for collecting, structuring and checking data of buildings (see 
Wang, 1994). The procedures used on both systems were 
very similar. Although the T10 offers automatic DTM 
generation, we did not apply it for the ITC model. The 
terrain being pretty flat, it was certainly quicker to measure 
a few spot heights along the streets and open areas. The 
only advantage of the DP in feature extraction experienced, 
was the stereosuperimposition which we do not have on 
the C120. Our curiosity, however, with the newer system let 
us to continue on the DP; the stereosuperimposition was 
not the reason. 
The production steps using the T10 were: 
define objects of interest (buildings, streets, ground 
surface) 
define level of detail (block level: global roof structure, 
vertical walls) 
design codes (see table 1) within capabilities of 
DEMETER 
digitize roof features and street edges with DEMETER 
and measure spot heights of terrain relief 
export coded points and line strings in DXF 
run model construction software 
interactively view reconstructed objects by TREVIS 
software 
import nodes and arcs from FDS via DXF in DEMETER for 
superimposition 
import DXF file in 3D-Studio for ray tracing and 
generating attractive pictures 
generate VRML file from the DXF file using shareware on 
Internet 
use WIRL for ‘walk through’ 
Figure 5 shows a screen print of the interactive visualization 
of our test site 'old ITC and its surroundings' by the VRML 
viewer WIRL. Figure 6 gives an example of a near realistic 
visualization of a designed object, the new ITC building, 
which was produced by in-house developed software. By 
now it would be possible to replace the facades of this very 
complex building (its model was constructed from 2D 
architectural plans) with photo true texture, since the real 
world building construction has just been finished this year. 
Meanwhile we also have developed a direct FDS - VRML 
translator, but have not experimented with including texture 
mapping yet. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996 
 
	        
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