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AUTOMATIC STEREO*
By G.L. Hobrough t
RESEARCH and DEVELOPMENT DIVISION
HUNTING ASSOCIATES LIMITED
Toronto,, Canada
This paper describes an automatic stereo
system using electronic image-scanning and
signal-handling techniques.! The system is
called Stereomat and was developed by the
author, at Hunting Associates Limited, as a
company-sponsored program. À paper describing
design details is shortly to be published in the
Transactions of the Engineering Institute of
Canada.
Stereomat utilizes the optical and mechani-
cal parts of a conventional plotting instrument;
parallax sensing is by electronic means, and
servo motors provide the motions necessary for
clearing parallax. Stereomat automatically per-
forms relative orientation, contouring, profiling,
and the plotting of drainage. It also assists the
operator during absolute orientation and the plot-
ting of planimetry. The production of ortho-photo-
graphs directly from Stereomat appears feasible,
and is expected in the near future.
Stereomat may be applied to most, if not
all, existing plotting instruments. However, this
paperis concerned principally withits application
to projection plotters. Application to non-pro-
jection and first-order instruments is dealt with
briefly.
The Engineer Research and Development
Laboratories of the United States Army have been
investigating automatic stereo plotting for many
years.“ They have expressed continuous interest
in the Stereomat program ever since it was an-
nounced and have recently acquired the first
available instrument.
Automation of stereo plotting has been ex-
pected for over a decade. Electronic computers,
information theory, and servomechanisms have
provided the essential techniques and components,
and it seemed reasonable to assume that the
basis for a workable system existed. Unfortu-
nately the extraction and utilization of image
information has remained a relatively neglected
field, except for recreating images as in tele-
vision.
Automatic Stereo Perception
A stereo perception system, human or
machine, performs the sensing operation of re-
lating corresponding points in two similar images.
Usually a reference mark or optical axis defines
a point in one image. Another mark or axis is
positioned, by the system, to register with the
corresponding point in the other image.
An automatic stereo system senses regis-
tration error or parallax and reduces it to an
acceptably low value by correcting the position
of the axes. The sensing of parallax should be
independent of the structure of the images, pro-
vided that there is sufficient detail to permit
recognition of corresponding points.
Scanning
The first step in the electronic process is
to translate each image into electrical signals.
This is done by scanning the images with a
*Presented at the Ninth International Congress of Photogrammetry, London, September 1960
T This publication is made without prejudice to any rights of the author, bis associates and
licensees concerning the subject matter in respect of which patent applications have been and may here-
after be filed in the United States and other countries.
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