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ric
chi
raf-
fic ‘accidents, industrial measurements
etc. They do not seem to offer to the
user the flexibility of a more general
approach and, indeed, the ability. to use
only part of the software.
For several years the Laboratory of
Photogrammetry of NTUA has been -endeav-
ouring to compile ‘a similar, vet more
flexible package. Thus FotoCAD, a modular
package was created. The various modules
have been developed and tested within
students' Diploma theses (Kavadas & Kvfo-
nidou 1988, Argiaditi 1989, Spinou 1990).
The structure of the system is presented
in Figure 1.
There are three main modules:
a. FullCal: The Camera Calibration Module
As the package is intended to be used
with metric as well as with semi-metric
or non-metric cameras a camera calibra-
tion facility was necessary. It offers
the possibility of a simple photographic
field calibration (Scott 1977,. Scott and
Georgopoulos 1979, Georgopoulos 1981).
The user simply needs to produce photo-
graphs of a linear array of targets along
the main lines of the camera format.
Simple measurements are also needed as
SURVEY
gum
FullCal |. Y 4 c
2
m 7 N
PHOS
Geodetic
Digitizer XYZ Data
Acquisition
Dr
Plotter
Figure 1
input to FullCal. The output of the mod-
ule are the radial distortion polynomial
coefficients and the shift of the origin
of symmetry (principal point), which will
be used directly as input parameters for
the next phase.
b. PHOS: The Photogrammetric Adjustments
Module
This module performs basic and advanced
photogrammetric operations to image CO-
ordinates (Kavadas and Kyfonidou 1988).
These image co-ordinates may have been
measured on a digitiser or a comparator
or any other measuring device. Interior
orientation is carried out using the rel-
evant information known about the camera.
Algorithms based on the collinearity or
coplanarity conditions are used for the
calculations. The user may select among
resection, intersection or relative and
absolute orientations. A minimum number
of control points with known co-ordinates
is required accordingly. Adjustments may
be done on single photographs or stereo-
pairs. The result of this module is an
ASCII file with tne object. co-ordinates
of all points observed. Appropriate codes
for use by the next module are also
attached to the points as early as the
image co-ordinate measurement stage. A
routine allowing for orientation of the
photographs without the need for control
points is currently under development.
c. Survey: The AutoCAD Restitution Module
A simple programme in AutoLISP language
has been developed in order to install an
appropriate command within the AutoCAD
environment, which will automatically
produce the plot on the screen for the
necessary editing to take place (Argia-
diti 1989). The programme uses as input
the previously created ASCII file. The
various codes attached to each point at
the previous stage will determine whether
it'is'a "single point, or a line point, or
a point “of ‘a circle, "or of an arc etc.
Further development of this module is
under way in order to incorporate the 3D
information and produce three dimensional
drawings.
3. THE PACKAGE UNDER TEST
Since several years the Laboratory of
Photogrammetry of NTUA is involved in
balloon photography expeditions using a
RAVEN TRF 600 balloon (Badekas et al.
1980). FotoCAD was tested using an
already existing stereopair from such an
expedition over the Minoan Palace of Mal-
lia (1500 BC) in Crete (Spinou 1991).
The photography was taken with a Hassel-
blad EL/M camera with a 80mm lens (nor-
mal) from a height of approximately 230m.
The original negative scale was 1:2800
with an overlap of 85%, which resulted to
an unfavourable, base-to-height ratio of
1:17. In addition, no control points were
determined at the time of the photography
(summer 1989) and this made the conditi-
ons of the test even more adverse.
