A software assistant for manual stereo photometrology
Date
1997
Authors
Sheer, Paul
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
A software package was written under the X Window System, Version 11, to assist
in manual stereopsis of multiple views. The package enables multiple high resolution
(2000 by 1500 pixels and higher) black and white photographs to be viewed simultaneously.
Images have adjustable zoom windows which can be manipulated with the
pointing device. The zoom windows enlarge to many times the resolution of the image
enabling sub-pixel measurements to be extrapolated by the operator. A user-friendly
interface allows for fast pinhole camera calibration (from known 3D calibration points)
and enables three dimensional lines, circles, grids, cylinders and planes to be fitted
to markers specified by the user. These geometric objects are automatically rendered
in 3D for comparison with the images. The camera calibration is performed using
an iterative optimisation algorithm which also tries multiple combinations of omitted
calibration points. This allows for some fault tolerance of the algorithm with respect
to erroneous calibration points. Vector mathematics for the geometrical fits is derived.
The calibration is shown to converge on a variety of photographs from actual
plant surveys. In an artificial test on an array of constructed 3D coordinate markers,
absolute accuracy was found to be 1 mm (standard deviation of the Euclidean error)
for a distance of 2.5 meters from a standard 35 mm camera. This translates to an
error of 1.6 pixels in the scanned views. Lens distortion was assumed to be negligible,
except for aspect ratio distortion which was calibrated for. Finally. to demonstrate
the efficacy of the package, a 3D model was reconstructed from ten photographs of a
human face, taken from different angles.
Description
A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand,
Johannesburg, in fulfillment of the requirements for the degree of master of
Science in Engineering.
Keywords
Aerial photogrammetry -- data processing, X window system (computer system)
Citation
Sheer, Paul (1997) A software assistant for manual stereo photometrology, University of the Witwatersrand, Johannesburg, <http://wiredspace.wits.ac.za/handle/10539/22434>