bul 2004
es of the
' (cell or
ontour of
polyline.
direction
t edge of
1e lowest
ages and
instituted
| vertical
1 face is
? contour
his is for
S.
ices have
le digital
dge from
of the
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B3. Istanbul 2004
2.4 Export of 3D models
Ones built, these 3D models are exported in form of topologic
models to a Topographic Information System or in different
CAD formats like DGN, DWG, DXF...
x XE
CEA AE >
WS x sa
P 00e
ho dd p PM
A et «
oF “die LE 5L
in 4 + A - dii b. n A
CINES YN. 3 x
Figure 4. Sample of exported model
3. DATA INTEGRATION IN A TOPOGRAPHIC
INFORMATION SYSTEM
The geometric data of the model are integrated into a
Topographic Information System as geometric datasets, graphic
datasets and topologic datasets. The differents datasets are
registered in a relational database structure. The topologic
integration is made while an internal data translation process.
The graphic data are structured in a tablesystem adapted from
the concept of 3D-FDS from Molenaar [1990]. (Figure 5).
OB) SE ORI TL OEJ P
s£ 14 [sfctass solace | I id [lclass] pid |pclass | md
+ | /
| f. \
F DE SF A DEL
[s [ndebut | nfın |
/
ARETE in id! x v t
: indi x1 y z
[oad Ics] ad [sens | vos dte Emm intent | A =
Figure 5. Graphic data model
The integration can be considered as a sort of step that allow to
formalise the graphical data of the initial poor graphical model.
4. TOOLS FOR ENRICHMENT OF THE FRONTAGES
This tool is the central part of the project implementation. It
will be used for the integration of supplementary 3D data in the
model and in the associated database.
In order to make this we decide to use images and photographs
(existent or to be shooted). In fact, it concerns the use of images
of the frontages of the different buildings from which we can
extract helpful information to enrich our 3D model. The
information which depends on the users point of view has to be
quantifiable. This implies the notion of measurement. Then it
seems to be important to provide the tools whith fonctions
allowing to measure directly on the photographed frontages.
549
The software package actually used for the visualization of the
models is Bentley-Microstation. This is the reason why we
continue to implement the new described tools onto this
platform. :
4.1 Image contribution
At a first time the asked question is the following one : outward
of the pure visual aspect of a photography, what are the
concrete information that can be extracted from the image of a
frontage ?
At first the number of stories can be counted, then their size can
be measured if the tool performs it. In a next step it will make it
possible to localize a significant recess which is not plotted at
the time of a classical approach of aerial photogrammetry. It
will be the same in case of balconies, loggias, porchs. On
another level, it will allow to identify shops, offices in the same
way as to define the allocation of the different stories
(habitations, shops, offices, etc). The postal addresses may also
be checked on this same way.
4.2 Objectives
The first objective is to permit the measurement of frontage
elements directly in the image. After this step is realized, it will
be possible to acquire some important informations like
described in the previous paragraph.
4.3 Measurement in the images
The aim was not to rewrite a tool for photogrammetric plotting.
In the developed system only one image at same time can be
used. The basic principle is that a frontage is a planar object and
whith this approximation we can estimate that one photography
can be sufficient to make some measurements.
4.3.1 Required conditions : the following equations define
the projective relation between two plans (1) :
bi.x+b2.y + b3
ee se Y =
b7.x + b8.x +1
b4.x + b5.y + b6
b7.x+b8x +1
When the 8 parameters bl to b8 are determined, these equations
allows to compute from the coordinates of a planar object
laying in a certain plan its coordinates in another plan. In this
case we can compute the coordinates of a given point in the
frontage from its image-coordinates measured in the
photography.
They are 8 unknown parameters, two data for each point (X, Y),
this implies that we have to know four couples of points in the
two systems. We have to know four points that we can digitize
in the image and for which we know the real position in a
coordinate system associated to the frontage.
4.3.2 Known points : It is necessary to know 4 points to
solve the system of equations and at same time compute the
eight parameters. But in our topologic 3D model each frontage
surface is described by four points. To make measurements in
the photography, the only requirement needed is that the
photography of the frontage contains these four predefined
points and allows to digitize them.
We can observe that the initial 3D model was obtained from
aerial photogrammetry. For better accuracy we have to take in
account the recess of the frontage from the rooftop counter line
we used to compute the vertical walls.
