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techniques for short baselines (under 7 km).
» applying 'on-the-fly' ambiguity techniques for
kinematic processing of GPS data.
The output from the KINGSPAD program will be used to
georeference (position and orient) the CCD images as
described in section 4.
CCD cameras produce standard video signals (e.g. RS-170,
CCIR). The CCD camera clusters used in the VISAT system
provide three dimensional positioning with respect to the
VISAT reference which in most cases is the perspective
center of one of the cameras. Recent trends in CCD cameras
are characterized by increased resolution and improved
radiometric quality. Use is made of sensor chips of
resolution 4k by 4k, with standard chips ranging from 400
to 580 lines and 500 to 780 sensor elements.
Determining the VISAT reference in three-dimensional space
is in principle a problem of trajectory determination. This is
equivalent to finding the six parameters that define rigid
body motion in space, i.e. three translations and three
rotations. The GPS provides three positions and three
velocities, while the INS provides three positions
(velocities), and three rotations. Therefore, the problem of
determining the VISAT reference can be seen as determining
six parameters out of 12 independent measurements.
3. HARDWARE CONFIGURATION
In the vehicle, the three sensors are interfaced to a regular
PC-AT, which controls the different tasks through
programmed interrupt processes. The PC has been designed
and assembled at the UofC with assistance by Logical
Solution Ltd. in Calgary. Figure (2) shows a block diagram
Lr
PPS 1 interrupt/sec
YIRQ7
oO
GPS - receiver
of the VISAT system hardware interfaced to the PC. The
VISAT hardware is controlled by a real-time data logging
software VIG (Video, Inertial, GPS) designed at the UofC.
The VIG has been written in such a way that in can
manipulate different hardware components. The output files
from the VIG software are the input to KINGSPAD software.
The VIG software performs the following functions through
an interrupt process:
* storing the INS position and attitude information at a
data rate of 64 Hz. The INS is interfaced to the computer
through the ARINC-429 serial board. At present the board
issues 64 interrupts per second through IRQ 5;
* storing the GPS position and velocity at a data rate of
2 Hz (2 k byte/sec). The GPS receiver is interfaced to the
computer through a smart serial board. With the smart board
the GPS data can be grabbed once per second, thereby
reducing the number of GPS data interrupts;
* storing the satellite ephemeries for post processing of
the GPS data;
* interrupting the computer time chip through the IRQ 7
upon receiving the PPS pulse from the GPS receiver. The PPS
pulse can be activated through any parallel port depending
on user requirements;
* storing any special events, e.g. start/end of ZUPT,
switch off/on the cameras etc., using the keyboard interrupts
through IRQ 1. All the interrupts throughout IRQ 1 are stored
on a file with time tag to allow post processing;
« grabbing and storing two or three simultaneous
images ( 0.5 M byte) every 0.4 sec. The program allows
different recording intervals for the cameras. The two CCD
cameras are interfaced with the computer through the
MATROX IMAGE-CLD frame grabber and the MATROX
IMAGE-640 baseboard. The IMAGE-640 works as a
temporary storage and an interface between the frame
grabber and the host. The IMAGE-640 has an EISA bus
interface which provides a full 32-bit data
ARINC:. 185-229
RS- 233 serial
Smart Board INS
64 interrupt/sec
Serial
Smart Board
IRQ 5
Monitor
Navigation Data
Monitor
Image Data
Keyboard
Figure 2: Hardware of the VISAT system
243
