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Title
New perspectives to save cultural heritage
Author
Altan, M. Orhan

CIPA 2003 XIX th International Symposium, 30 September - 04 October, 2003, Antalya, Turkey
close up top images are obtained. The camera was lifted with a
tripod to provide top images. However, the recessed portion of
the top floor and the roof could not be well documented since
lift-support and aerial photogrammetry were necessary for these
work. Apart from close ups, overviews were taken. Overview
images are not for measuring, but they cover the façade in a few
photographs and help one to orient himself within the image set.
Apart from multi-image technique, single image rectification is
selected to be used for the photogrammetric plotting of the
details. For this process, the digital camera was used. Since
these images were for texture mapping and orthophoto
production, it was important to shoot them with minimum
perspective possible. Within this frame, unit areas between
every two pilasters (6,5 x 14 m) were documented in a single
photo taken from the ground level.
4. PRODUCTION OF PHOTOGRAMMETRIC MODEL
In order to produce the photogrammetric model; first, the metric
images were digitized on a desktop scanner. Then, these images
were evaluated with an image evaluation software.
4.1 Scanning
Photogrammetric evaluation in desktop environment requires
images in digital format. Films shooted with reseau metric
cameras are best suitable for scanning because of the possibility
of controling image deformation caused by the scaning process.
A wide range of high quality image scanners with high optical
resolution, good geometric quality and color depth with 14 bit
for each color is available. In short, large film formats with a
reseau in combination with desktop scanners with high
resolution provide good results (Pomaska, 2001).
imago 2
good intersection angle
Figure 3. Principle of taking metric images
In this study, films shooted with Rolleiflex 6006 metric reseau
camera were scanned on AGFA Duo Scan T 2500. With this
scanner, a resolution of 2500 ppi can be reached. The object
size in regular images was approximately 15 x 15m. This
corresponded an image size of 60 x 60mm. Therefore, the image
scale was calculated as 1/250 (15 000 / 60 = 250). According to
the scanning theorem (Luhmann, 2000), 5mm should be taken,
if 10mm is the aimed object resolution. Then, the result of the
calculation 15 000mm (object size) divided by 5mm (object
resolution) is 3000. This is the number of pixels. The end-
product of the scanning process will be 3000 by 3000 pixels in
size. This is around 1000 dpi. For getting a unique image
resolution, the object resolution was selected with 0.005m. A
surface of 15x 15m is then given with a resolution of 3000x3000
pixel. On the other hand, the production of good colours in the
scanned images requires the calculation of a profile for the
scanner. Here, scanning was carried out in RGB colours. For the
improvement of the images via the image processing program
Photoshop, gamma correction of 1.5 and sharpening was made.
Image files were named considering film numbers and image
numbers, and saved as bitmaps.
4.2 Evaluation of Images
There are various software for evaluating metric images. In this
research, CDW (Close Range Digital Workstation) was used for
the evaluation of metric images. This software provides aid in
image refinement. Correction of photo coordinates is known as
image refinement. Image deformation results from different
sources. These are lens distortion and geometric deformations
such as lack of film flatness or orthogonality (Atkinson, 1996).
CDW handles the correction of lens distortion and geometric
deformations. At the same time, the software measures image
coordinates (Pomaska, 2001).
In this study, library of images for left, middle and right parts
(see section 3.2.2) was developed. Scanned images were saved
in their correct folders. Evaluation of each library (part) was
carried out separately; then, the results were combined. The
following process was repeated for each set in CDW
environment:
1. The system fixing table was filled in. From the
control points, measured with a total station, seven
values for defining the degrees of freedom for a co
ordinate system were selected and entered in the
system fixing table.
2. Camera data was introduced: 6050 middle format,
reseau 6006, focal length: 51.24, XH: -0.25, YH:
0.16, rO: 20, angle unit: GON.
3. Images were oriented. During this process, the reseau
crosses were utilised. The crosses at the four corners
of the central cross were checked in. This gave way to
an automatic selection of the rest of the crosses. If
more than 50% of the crosses are oriented
automatically, the transformation is considered as
sufficiently accurate. In turn, the image file is saved.
4. Image coordinates were measured. Images
documenting the same sub-section of the building
surface were grouped together. At least two images
viewing the same area with a different perspective is
necessary for measurements (see section 3.2.2). Then,
‘measure image coordinates’ was chosen on the
toolbar. Six matching points that are observed on the
images of the sub-section worked on are marked. For
example, left top corner of window A is marked in the
images viewing it. The six points should be
distributed evenly on the selected elevation portion. In
addition, these points should not belong to the
shadowy and hidden areas.
5. Object coordinates and camera positions are
calculated. Theoretically, this process is composed of
a series of resections followed by intersections