6.3. CAAD-model
The result of the photogrammetric processing is a three-
dimensional geometric and semantic object description,
which can be passed automatically via LISP-files to the
CAAD-system. This system is able to preprocess the data
and store it in data structures adapted to architectural pur-
poses. The system is capable to find efficiently special
data in a huge data base. It allows data transformation
into other representations in an casy way. The task of the
architect is just the creative finding of new solutions or to
judge the current solution. The CAAD-system is impor-
tant for documentation and visualization, and for com-
plex simulations, manipulations and analysis of the
object. This could be used in art history, in preservation
of historical monuments and sites, in regional and local
planning, as well as in renovations and reconstructions.
Figure 9 illustrates a parallel perspective view of the pho-
togrammetric generated CAAD-model of the church. The
existence of a surface model is demonstrated with the
shaded representation.
6.4. Precision of photogrammetric analysis
The precision of the photogrammetric analysis is as-
sessed in two ways. First the theoretical precision of ob-
ject coordinates was determined with a bundle
adjustment. The results of the adjustment are given in ta-
ble 1. The coordinate system was defined with X- and Y-
axis in the plane of cach facade and Z-axis in depth. The
results indicate for the Canon CI-10 a precision corre-
sponding to 1/3" of the pixel spacing in image space. The
theoretical precision of the object point coordinates is
Figure 9: CAAD-model of church Giova (imagery from Canon CI-10).
2.1 cm within the plane of each facade and 4.0 cm in
depth. The Rollei 6006 imagery delivers a theoretical
precision of the object point coordinates of 1.3 cm within
the plane of each facade and 1.3 cm in depth. This corre-
sponds to 3.1 um in image space. Here the analogue sys-
tem seems to be superior, but this solely due to the much
higher resolution of the imaging system. The results of
the digital system are very encouraging when considering
the low resolution of the still video camera used.
Table 1: Precision of photogrammetric analysis
Imaging system rer Ss
Canon CI-10 100 1.8 1.0 4.0
Rollei 6006 112 0.9 0.9 1.3
Digitized images 112 0.8 0.9 1.2
The main difference between the digital and the analogue
system is not the precision of photogrammetric process-
ing, but the architectural details which can be measured.
This was demonstrated in figure 6 and can also be shown
in zoomed parts of the resulting CAAD-models. Figure
10 shows the front facade generated with the analogue
Rollei images (figure 10.a.) and comparable parts of the
models generated with digital (figure 10.b.) and analogue
techniques (figure 10.c.).
What is to be expected with a digital imaging system pro-
viding a resolution comparable to analogue film is dem-
onstrated with the digitized images of the Rollei 6006.
The theoretical precision of the object point coordinates
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