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.
E SURFACEO LINEOBJ POINTOBJ
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= T
ARCONF ARCPOFL | NODE
| gerer]
L E | apartofl -
nid | xc|yc | ze |
| M ARC )
| [si bidleft ET =e | arcbeg =)
|
| EDGE acu ÍNODEINB NODEONF
fid | enoseq | |arcid | forback | arcid ja | bir nisinb | | nid 23 |
|
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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
