379
bandwidth but poor modula-
1 purposes this test will rank
l for that purpose the author
surpassed by any other test,
isolated detail can be seen,
: and proven test which will
the past few years have not
valuation of a system or the
ave greatly improved our
f image quality, so that we
valuation technique can or
>GMENT
f Itek Corporation’s per-
The opinions expressed are
:hor, but their development
evitably been influenced by
gues at Itek and (formerly)
iment, and with Professor
1 programmes sponsored by
¡ted States Air Force under
L To all of these grateful
CES
i. Special Congress Number B.
is given by Perrin. Perrin, F. H.
neers, 69, 151, 239 (1960).
'ournal of Photographic Science, 10,
'ourth Engineering Report. Itek
A.ir Force.
IMAGE LOCATION
By R. W. Fish
Ministry of Aviation
(Invited Paper, Commission I, Xth International Congress of Photogrammetry,
Lisbon, 1964)
Abstract
An account is given of the source of position errors in air photography,
with particular emphasis on results reported since the I960 I.S.P. Congress
in London. Some proposals are made for work to be done.
1. Introduction
In the last fifteen years or so there has been a revolution in the optical performance
of air cameras, largely due to the introduction of the Aviogon lens and its later
competitors. With an improved resolution right to the edges of a 90° field, it has
become possible to locate images with greater precision, and gradually the photo-
grammetrist has come to expect greater accuracy from his negatives. At the
Symposium of Numerical Photogrammetry in Milan 113 there was considerable
discussion on the need for greater accuracies in the photography. Residual errors of
about 20 ¡x were mentioned as being found in “good” photography, while the makers
of plotting machines have provided a measuring accuracy of perhaps 2 p,. The
situation is, however, now rather different from any we have met in the past, in that
there are a large number of possible sources of these residual errors, each of which
can contribute a few microns. The camera maker must therefore make significant
improvements in many directions if the total error is to be reduced to 5 /x or less.
The present paper reviews recent work on these sources of error, concentrating
on developments reported since the 1960 London Congress.
2. Basic Geometry of Image Formation
As in many branches of science, the basic concepts of image formation present
difficulties in definition when applied to real systems which are far from perfect.
These difficulties continue to provide opportunities for discussion, but for our
present purpose it is only necessary to present a simplified account of the subject.
Image formation is a process which transforms an object point (R, 6) in
polar coordinates on a plane earth into an image point (r+Ar, 6+ Ad) on a plane
negative. By definition there is a constant relationship between R and r over the
entire negative given by
R = kr = HrIF (1)
where k is a constant
H is the aircraft height
F is known as the principal distance
Ar is known as the radial distortion
r/\9 is known as the tangential distortion.