the slide to the
e figures 2 and
similarity trans-
nsformation) -
(1)
'ed image.
ion from slide-
s on Pro Photo
4
——
ormation from
ligitized image-
the residuals in-
s, which are not
her comparisons
2nd order poly-
as much signif-
This is because
Q2
the Helmert-transformation is not sensitive to different scales
in z- and y-direction (Baumann, 1985). And this might be
caused by the two different resolutions of the ScanMaker 45t.
Such systematics can't be seen the images of the Pro Photo
CD.
A visual comparison of the images maintains this results. Fig-
ure 4 shows an artificial control-point, which is part of an im-
age produced from a slide by Kodak's Pro Photo CD service.
Figure 5 shows the same detail in the same slide digitized
with ScanMaker 45t.
Figure 4: Image with artificial control-point produced by Ko-
dak's Pro Photo CD service.
Figure 5: Image with artificial control-point digitized with
ScanMaker 45t.
Also Figure 6 and 7 allow a visual comparison of a natural
control-point.
But another important fact are the costs of a digitized image
especially for large amounts of images. It has to be considered
if it is less expensive to buy a scanner than to pay for the
images of a Pro Photo CD. At the moment the costs of the
MicroTek ScanMaker 45t compared with the Pro Photo CD
service are amortized after 200 pictures. And Kodak can't
guarantee how an individual service provider maintains the
equipment and handles the original film.
It would be good to reduce the afford of developing and dig-
itizing by using a CCD-camera. Therefore it would be a bet-
ter solution for rapid processing to get a CCD-camera with
a sufficient accuracy in geometry and resolution and with a
suitable price.
The digital image is the base for all further steps like radio-
metric and geometric image analysis and correction, bundle
block adjustment and it is also a good way to store the image
data without the danger of fading colours. This is why digital
photogrammetry has to be used, especially on the background
of large amounts of data.
311
Figure 6: Image with natural control-point produced by Ko-
dak's Pro Photo CD service.
Figure 7: Image with natural control-point digitized with
ScanMaker 45t.
2.3 Image Rectification
One field of activity in photogrammetry is to produce or-
thophotos of given facades. This can be achieved by a differ-
ential rectification of an image. But this requires the knowl-
edge of the 3-dimensional model of a facade.
Under the assumption that a facade of a building is plane
— what is sometimes very cruel and oversimplifying, but on
plane buildings and facades a good approximation — a simple
projective transformation of a plane can be used. The errors,
produced by parts of the facade which are not in this plane, or
by discontinuities, can be reduced by a part-wise rectification
(Pallaske et al., 1992). For this approach the facade has to
be subdivided into small pieces.
If the facades are too big for one single photo, or the rectifi-
cation is done piece by piece, the resulting images have to be
joined together by mosaicing (Heinz, 1996). This has been
done using control-points to determine the coefficients for a
projective transformation (Figure 8). In this task care and
attention has to be paid to the equalization of the brightness
and colour differences inside and inbetween single images.
2.4 Additional Information
In a second stage it is necessary to gain additional information
for the creation of an urban information system.
This additional information consists of geo-referenced al-
phanumerical and graphical data.
Alphanumerical data consists of informations about special
objects like buildings (age of the building, number of resi-
dents, date of last restoration, etc.), where as graphical data
denotes images of objects, resulting orthophotos, representa-
tion of 3-dimensional models, etc.).
Archiving and representing alphanumerical data is a com-
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996
