reseau reseau
d \ film
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pm Photogram
retro - reflector
es | si
ait Na lens
ring - strobe
Fig. 3 Illumination and recording of retroreflective targets
All the camera operations are microprocessor-
controlled. Exposure time, réseau exposure level and
exposure number can be selected and/or displayed on
a remote control panel (Fig. 1). A complete exposure
cycle effected by pressing one control key includes
film flattening with vacuum pump, réseau illumination
and exposure, object illumination with flash light and
object exposure, and film transport. The power supply
is accomplished by rechargeable batteries.
4, RESULTS OF TEST MEASUREMENTS
In order to prove the practicality of the R_METRIKA
and to analyse its accuracy, a test range was
photographed several times using both the wide angle
and the normal lens cone. The image blocks included
8 photographs taken from 4 camera stations in a
convergent imaging geometry. At each station two
images rotated about the camera axis by 180° were
produced. The photographs then were measured in
the Réseau-Scanner RSI, ie. the target centroids
were determined automatically by image processing
algorithms (see Luhmann, 1988).
The photogrammetric triangulation performed by
self-calibrating bundle adjustment resulted in RMS
values of the residuals of image coordinates of 0.8 um
(x) and 0.7 um (y) for the camera equipped with
normal lens. Corresponding values for the wide angle
lens amounted to 1.0 um (x) and 0.9 um (y). 3-D
coordinates of the targets were determined with a
standard deviation of sy = sz = 0.014 mm and
sy = 0.035 mm (Y perpendicular to the test field
wall). In relation to the object diameter of 5.5 m, this
means in any case a relative measurement accuracy of
clearly better than 1 part in 100,000.
5. FIRST APPLICATIONS
The R METRIKA imaging system is applied at the
European Space and Technology Center. The ESTEC
is engaged in high accuracy geometric quality control
of large spacecraft structures, antenna reflectors etc.
These components are tested in a Large Space
Simulator (LSS) to examine the influence of space
conditions. Measurements in advance and after a test
give evidence of non-elastic alterations, e.g. caused by
temperature variations resulting from different
illumination levels.
N
CN
réseau- d
illumination =
Fig. 4 Illumination for réseau projection
Table 2
TECHNICAL DATA R METRIKA
Type Single lens rollfilm camera with viewfinder,
film flatness with vacuum pump system and
réseau technique, microprocessor-controlled
camera functions, user panel, data back, ring
flash, réseau pre-illumination, rotation ring
Format | 4x5"
Film 5" (126 mm) rollfilm
Réseau mesh width in x and y: 2.0 mm
Lens 1) 75 mm Schneider Super Angulon
5.6 / 75 mm metric
(angle of view: diagonal 105 deg.)
2) 150 mm Schneider Apo-Symmar
5.6 / 150 mm metric
(angle of view: diagonal 70 deg.)
Weight ^ camera body with rotation ring and ring flash
approx. 9500 g,
external accu unit approx. 1000 g
Size approx. 300 x 300 x 300 mm
In addition, elastic deformations which occur during
successive test phases are to be determined by
photogrammetric survey in the interior of the LSS.
Simultaneous release of three or more cameras is
necessary to record the object changes. The cameras
are built into protective housings to keep them free
from vacuum and simulated space conditions. A front
glass plate allows the view inside the LSS. The objects
to be surveyed have a diameter of e.g. 6 m.
Simultaneous recording of 100 to 500 points is
required to yield reliable quality control.
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