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5.2.2 Application with digitized images 
In addition to the application mentioned in the previous section we present at this point some investigations which were 
attained with an interior clay design model. The model represented the interior side of a car door. Analog photos were 
captured with a stereo middle format camera at a distance of 1.5 m and a base-to-height ratio of 1:3. The focal length 
was 100 mm at a net photo format of 12 cm x 9 cm. The cameras were arranged in the conventional normal case. The 
analog photos were digitized on a PS1 scanner with a pixel size of 15 um. Thus, the pixel size on the object amounted 
approximately to 0.22 mm. Control points were provided by a CMM machine. 
Since no independently measured reference data were available for that setup, we used profile measurements which 
were derived from the same digitized stereo pair. Theoretically, their measuring precision amounts to 0.070 mm, as- 
suming a parallax precision of 0.1 pixel. These measurements were interpolated into the facets of the point cloud 
measurements being also derived from the digitized stereo pair. Their measuring precision could be estimated to ap- 
proximately 0.10 mm presuming 30-40 matched points per single finite element mesh. Since both measurements refer 
to the same orientation and the profile measurements are more accurate, the profile measurements could be used to 
check the internal measuring precision of the point cloud measurements. Table 4 shows the results of this investiga- 
tion. ; 
The comparison of the figures in table 4 shows again a good correspondence between the theoretical standard devia- 
tions (70 ,,) and the empirical standard deviation (7r.m.s.). Also, the internal precision estimate |, confirms those 
values. The investigations show for this application that a full scale model could be digitized by the point cloud option 
with an measuring precision of about 0.11 mm. 
The comparison of the values in 5.2.1 and 5.2.2 show that almost the same precision could be obtained on the object. 
This is mainly a matter of the pixel size on the object and the geometrical camera configuration. However, the size of 
the workspace of the two setups is considerably different. It amounts for instance for the Kodak DCS 200 stereo cam- 
era to approximately 50 cm x 50 cm. In contrast, the net stereo coverage of the middle format camera pair is in the 
order of 1.2 m x 1.2 m. Hence, 4-5 times more DCS 200 images have to be captured in order to cover the full scale 
model. In view of the related complex photo triangulation and the number of small surface parts to be derived sepa- 
rately, this appears too time consuming and thus uneconomical. 
5.3 System performance 
At the end, we should mention numbers which reflect the system performance. The measuring speed is mainly a 
matter of the workstation in use and amounts - in case of the Indigo2 - for the point cloud generator to 50 3D 
points/sec and for the profile measurement option to 25-30 3D points/sec. 
More important for the practical acceptance is the time amount which is needed for the complete measurement of a 
concept model or a full scale clay model, respectively. So far, we have rough numbers for the combination of the sys- 
tem with the Kodak DCS 200. A 2096 concept model could be fully covered with about 10 stereo models (= 20 images) 
presuming the same stereo camera configuration like in 5.2. Altogether, it could take 1.5 days to digitize the complete 
model including the single process steps object preparation (1 h), image capture (2h), data transfer (1.5h), photo tri- 
angulation (2h) and surface measurement (2h - 3h). No post processing in a CAD system is included in this estimate. 
The point density would be in the order of 5 mm on the object. Thus, approximately 15000 3D points would cover the 
object. Apparently, most of the time saving is gained by the fast digital image capture which can be processed imme- 
diately. 
6. CONCLUSIONS 
The investigations of the paper show that the presented digital photogrammetric measurement system for automatic 
surface reconstruction, together with a new bundle adjustment package, can successfully be applied for the digitizing 
of design models. Especially, the combination with a today's still video camera Kodak DCS 200 makes it appear as 
highly attractive for concept model digitization. The achievable measuring precision on the full scale model seems to 
be sufficient for modern car design strategies. The new Kodak DCS 460 with a 2000 pixel x 3000 pixel sensor will in- 
crease the flexibility of the system with regard to the size of the working space. ; 
7. REFERENCES 
Agouris, P. 1992. Multiple Image Multipoint Matching for Automatic Aerotriangulation. Ph.D. Dissertation, Department 
of Geodetic Science & Surveying, The Ohio State University. 
Baltsavias E. 1991. Multiphoto Geometrically Constrained Matching,. Ph.D. Dissertation, Institute for Geodesy and 
Photogrammetry, Report No. 49, ETH Zurich. 
IAPRS, Vol. 30, Part 5W1, ISPRS Intercommission’ Workshop “From Pixels to Sequences’, Zurich, March 22-24 1995 
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