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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B1. Istanbul 2004
The panchromatic part of the camera combines a set of 9
medium format CCD sensors into a large format panchromatic
image. The multispectral channels are supported by four
additional CCD sensors.
Each of these 13 CCD sensors is the front end of a separate
imaging module. It consists of the sensor, the sensor
electronics, a high end analog/digital converter (ADC) and the
IEEE 1394 data transfer unit.
The raw image data is transferred via the IEEE 1394 interface
to a separate storage module of the Storage and computing Unit
of UltraCamD.
Thus the camera offers a frame rate of more than 1 frame per
second, exploiting the benefit of its parallel system architecture.
The panchromatic image consists of 11500 pixels cross track
and 7500 pixels long track. Color is simultaneously recorded at
a frame size of 4k by 2.7 k pixels for red, green, blue and near
infrared [Leberl 2003].
2.2 Multi-Cone Design of the Camera Body
The geometric performance of the camera is defined by the so-
called “master cone”, which consists of four CCD sensors and
one single optical system. The four CCDs define the large
format panchromatic image of the UltraCamD. The gaps
between these four sensors are filled by the other three
panchromatic cones. The transformation between cones is
determined by the calibration and is being confirmed on line,
ie. for each frame, by tie point matching. We denote the
merging of the individual image segments into a full-format
image by "stitching" (Figure 2).
MASTERCONE with 4 CCDs MASTERCONE plus Cone # 2
MASTERCONE plus Cone # 2 and 3 MASTERCONE plus Cone # 2, 3 and4
Fig. 2: The backplanes of four cones of the panchromatic
channel produce a set of 9 sub-images. These get sequentially
grouped in 3 steps, where 4 formats exist, which we denote as
“layers”. The master cone on the upper left with its 4 CCDs
defines the geometry of the large format image.
3. CALIBRATION TARGET
The calibration target is established in a room in the basement
of Vecxel's office building. Its dimensions are 330 cm by 220
cm by 200 cm. Three fixed camera stations are available.
43
The target consists of 240 well defined points, surveyed at an
accuracy of +- 50 um in X, Y and Z. The points are fixed on the
rear wall, the sidewalls, the ceiling and the floor.
Four additional points are established in a central position of the
target volume (Fig. 3).
Fig. 3: Calibration test field in the basement of Vexcel's office
building. The test field consists of 240 precisely surveyed
control points.
3.1 Data Capture
The data capture, i.e. the taking of images with the camera, is
done from the three camera stations. Tilting and rotating the
camera leads to a set of images from each station. In such sets
we derive high redundancy and excellent distribution of
measurements in the image plane. Exposure time and aperture
of the lenses are tuned for the specific application. In order to
derive a reasonable sharpness in the images at a limited object
distance, a small aperture, (f 1/11) and a rather long exposure
time of 3 sec is chosen.
A set of 84 images is taken from three image stations by
rotating and tilting the camera .
s 330 cm * 240 cm * 240 cm "
à
Fig. 4: Three Camera positions are established (left) and a set of
84 images is produced by rotating and tilting (right) the camera.
3.2 Image Coordinate Measurement
The image coordinate measurement is supported by special
software tools. For the manual approach a zoom window is
displayed and control point positions are measured within steps
of a quarter of a pixel. The final set of image coordinates of the
