THEORY AND DEVELOPMENT OF AN ON-LINE 30 Hz VIDEO PHOTOGRAMMETRY
SYSTEM FOR REAL-TIME 3-DIMENSIONAL CONTROL
Dr. H.F.L. Pinkney
Engineering Physics, Structures and Materials Laboratory
National Aeronautical Establishment
National Research Council of Canada
Ottawa, Ontario Canada K1A OR6
ABSTRACT
A 30 Hz Video Photogrammetry System for 3-dimensional machine control tasks, such as a
Manipulator System of the kind used in the Space Shuttle, has been developed at the National Research
Council of Canada. Based on the moment description for the two-dimensional distribution of a two state
variable, the areas and first moments of the level discriminated video signal are derived on-line at 10 MHz
with the scan for each of four computer controlled window apertures.
During the 1 ms fly-back of the video, for each frame, the area and moment data from the
on-line moment sampling processor are transferred to a high speed mini-computer, the centroids calcu-
lated and the window aperture positions changed to maintain tracking and sampling of four moving
target areas. The centroid data for four targets on a rigid body permits the single camera solution to be
solved for each frame to determine the position and orientation of the body for 3-dimensional machine
control.
Because of the on-line moment sampling processor, less than 20% of memory space and less
than 20% of available computing time of the mini-computer are utilized for the photogrammetric
system leaving the remaining 80% for machine control tasks. Typical centroid data with a commercial
camera show standard errors in the photo-co-ordinates of the order of one part in 5000 of frame size
>3 pm.
A low pressure sodium source beam-splitter multi-cube corner target system permits reliable
measurements independent of ambient lighting conditions. The moment sampling processor can also
be used to track and measure lines, edges and corners for single or multi-camera set-ups, thus providing
for other photogrammetric applications.
INTRODUCTION
An on-line 30 Hz video photogrammetry system for real-time 3-dimensional control is
currently being developed at the National Research Council of Canada. Based on the moment de-
scription for the two-dimensional distribution of a two state variable, an NRCC developed moment
sampling processor* derives at 10 MHz, on-line with the video camera scan, the areas and first moments
of the level discriminated video signal within each of four computer controlled window apertures.
Interfaced with a mini-computer, the data from this sampling processor permits the determination of
the photo co-ordinates (centroids) for four targets on a rigid body and the single camera solution to
be solved, each frame, to determine the position and orientation of the body with respect to the
camera.
The development of this system originated in response to a conceptual problem arising from
Canada’s involvement with the U.S. Space Shuttle program; notably in relation to the design and
building of a six degree-of-freedom anthropomorphic arm for the deployment and retrieval of
satellites. The essence of the question was: Given the existing limitations of positional information
available to the operator due to limited angles of direct view and the flatness and resolution of the
closed-circuit television camera view, how could one provide, if necessary, better spatial information
for the position and orientation of the satellite during capture with the End-Effector of the arm and,
after capture, during its berthing in the Shuttle Storage Bay?
* Patent applied for
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