1.3 Available Photographs
Fortunately a series of amateur colour 35 mm slides were made
available to us by two Israeli archaeologists. They happenned to
have recently flown over the Old City with a small handheld
camera. They appreciated our problem and kindly made copies
of their slides for us. A sample of one such amateur image is
shown in Figure 1.
Figure 1: An oblique photograph of Old City Jerusalem
2. DATA AVAILABLE
2.1 Geometric Documentation Products
In order to achieve the desired result, all available data should
be exploited. At our disposal were all drawings produced for the
geometric documentation of the complex. They were plans and
elevations at a scale of 1:50, both in analogue and digital form
(Figure 2).
Figure 2: Sample of the geometric documentation drawings
Moreover we also had access to all our relevant geodetic
measurements and other technical data, such as point co-
ordinates, angles, height differences and three dimensional
distances.
2.2 Image Data
Nothing was known, however, concerning the geometry of the
35mm slides available. They were taken with an amateur, but
completely unknown, camera obviously equipped with a zoom
lens. Hence the images were of different and unknown scales
taken with various and unknown focal lengths. Moreover, as the
camera was handheld, the images were taken at completely
uncontrollable angles. Additionally, the copies made available
to us were made with unknown process, a fact which may have
caused even worse geometry problems. However, a rough
estimation of the mean image scale for these photos was
possible with the help of some known distances appearing on
them.
3. METHODOLOGY
3.1 Exploiting the available data
Since the only information available were these particular
images, it was decided to try and exploit them to the best of our
abilities (Modatsos, 2000).
It was decided to implement an adjustment method, which
would be able to calculate and determine practically everything,
under certain circumstances, of course. This method is none
other than the bundle adjustment method. As output products
one may receive co-ordinates of unknown points, co-ordinates
of image stations, camera lens attitudes and, of course, the
interior orientation parameters of the cameras used. In such an
adjustment the additional information available would be of
utmost importance.
3.2 Software Description
For the adjustment the BINGO-F v.4 software was available. It
is a well known bundle adjustment software with long presence
in the market and very good reputation. The characteristics of
this software are briefly the following:
Complete parametrisation
Full control of all unknowns and observations
Possibility to perform self calibration
Possibility for inclusion of geodetic measurements in
the adjustment
Ability to adjust images irrespective of their attitude
No need for ground control points
Complicated data snooping techniques
No need for initial approximations, as the software
calculates them automatically
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For the calculations BINGO-F uses the well known collinearity
equations and as input data it requires the image co-ordinates of
all known or unknown points appearing on the images, the co-
ordinates of the ground control points, the eventually known
geodetic measurements (e.g. distances) and all the necessary
parameters for the interior geometry of the camera (Kruck,
1998).
As output the software provides the co-ordinates of the
perspective centres and the camera axes attitudes expressed
with the help of the Euler angles, the co-ordinates of all
unknown points involved in the adjustment and — if so required
by the user — the parameters of the interior geometry of the
cameras, i.e. the principal distance, the coefficients of the radial
distortion curve and the image co-ordinates of the principal
point.
3.3 Data preparation
In order to implement the adjustment, a preparation stage was
necessary. The images available were enlarged and used in
order to determine those detail points which would be necessary
to produce the roof top plan. This operation resulted to a
detailed sketch of the roof tops which was constructed with the
help of the already available drawings, but also with the help of
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