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art B5. Istanbul 2004
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part BS. Istanbul 2004
measured. Ten control distances in the range of 1.6 to 6.0 m
have been measured and compared with the distances calculated
from the photogrammetric survey (see Tab.3). As the geodetic
measurements have been carried out only with a measuring tape
the accuracy of the distances is to be considered in the area of
+/- 5 mm.
Control Distance m]
length | difference
1 1208-518 3.590 -0.010
2 1207-528 3.910 -0.020
3 1206-526 3.550 -0.029
4 223-225 6.048 -0.014
5 801-802 2.800 -0.016
6 285-296 3.760 -0.012
7 083-073 2.020 0.011
8 415-053 3.470 0.013
9 445-311 1.590 0
10 310-017 2.201 0.009
Table 3. Calculated distance differences
Depending on poor intersection angles some of the control
distances could be triangulated only with low accuracy. The
mean absolute difference of 13.4 mm was sufficient for the
whole photogrammetric project.
4. DISCUSSION
4.1 Comparing Analogue with Digital Measurement
In comparison to the analogue imaging and photogrammetric
measurement process the digital method requires many more
images depending on the resolution of the digital cameras and
the geometric conditions in the museum hall. In 1982 forty
stereoscopic image pairs were necessary for the production of a
line drawing of the wooden surface of the cog. For the
measurement of the profiles only ten vertical lines had to be
projected onto the surface from both sides of the cog (see fig.
5). Those lines were measured in stereo mode with the
Stereoplanigraph C8 and were drawn in real time at a
mechanical plotting table.
Figure 5. line drawing with profile lines
In the second measuring campaign in 2003 over 99 images were
necessary for the triangulation. 227 tie points and twenty
signalised profile lines were required to offer enough points for
the monoscopic measurement in the convergent images.
The profiles exist of 340 measured points. The image
coordinates of these points have been measured in manual mode
with the pointing device of the PC.
An overview of the camera stations, profiles, control distances
and measured points is given in figure 6.
Figure 6. camera stations, profiles and control distances
Although the whole object reconstruction could be carried out
with a standard PC and without the need of a digital stereo
workstation the required accuracy between 10 and 20 mm in
object space could be reached. The software PhotoModeler 5.0
Pro from Eos Systems Inc. offered following functions for the
photogrammetric data processing:
e Camera calibration,
* Project image administration,
e Manual and automatic image coordinate
measurement,
* Epipolar line referencing mode,
e Definition of points, lines, surfaces and textures,
e Photogrammetric bundle adjustment,
e Measurement of three dimensional coordinates
and distances,
e Visualisation of three dimensional data,
e Ortho image production,
e Vector and raster data export.
The statistical point reports and the residual display were very
powerful for the detection of registration errors and poor
intersection constellations.
The ability to consider several project cameras was important
for the common adjustment of all images from both used digital
cameras.
4.2 Analogue to Digital results
In 1982 line drawings and profile plottings in the scale 1: 20
had been produced. The line drawings were produced for both
sides of the cog and also for an inside view. The details shown
in the drawings depend on the ability of the operator to do an
interpretation of the image material and to select important
features and draw them. As this was a very time consuming and
expensive method today in most cases ortho image maps will be
preferred.
Therefore in 2003 no line drawings were asked from the
customer. Only the profiles were delivered on paper as well as
digital data sets again in the scale 1 : 20.
For publication purposes additional three dimensional
visualisations with textured surfaces and ortho images have
been processed. One of the historical line drawings can be
compared with a part of an ortho image in figure 7.
