Vertical Parallaxes, Lens Distortion and
Stereoscopical Model
By Dr. Percy Tham, Stockholm*)
Abstract
The geometric conditions of the central perspective of the photo-
grammetric picture are decisive of the accuracy of the measurement.
One of the most important optical lacks has been, and still is, the lens
distortion. In general, at the photogrammetric stereo-treatment this
distortion has to be compensated for.
In view of present-day requirements for great accuracy, no lenses are
to be considered as free from distortion. On the contrary, even lenses
of specially high quality need a compensation of the distortion when
used for large-scale mapping.
To-day, all photogrammetric cameras are subject to a meticulous exa-
mination in the laboratory before delivery and the lens distortion is
measured and given as a lens distortion curve,
However, in practice such an examination is not always possible to
repeat continously in a laboratory. For that reason also test fields of
various types are used for checking the camera calibration.
Besides, methods have been developed to determine the lens distortion
by means of a study of the geometry of the single picture.
Into a lot of papers to the VIII. International Congress and there-
after, the method of studying the residual parallaxes of the stereo-
scopic model as a feasible way to improve the relative orientation of
the pair of pictures, approximately vertical, has been introduced.
Moreover, the idea has been examined to use the residual vertical pa-
rallaxes to calculate the lens distortion curve in a reversal way. That
means that the residual vertical parallaxes remaining from the relative
orientation alone should be sufficient for a determination of the lens
distortion curve, independently of the original amount of these paral-
laxes. In the technical reviews of the last years, examples of lens distor-
tion curves illustrate the application of this idea.
However, objections have been reaised against this idea on the whole.
*) This paper has been published by courtesy of LAMCO Joint Venture and
SENTAB, consulting civil engineers to LAMCO.
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