CAMERA CALIBRATION CONSTANT
i TS
Jd. A, Eden
Precis
It is advocated that whatever information is provided on a
calibration certificate the basic measures of x and © should always be
included.
OFTEN NT DAT RAT EEE ANREDE EHEN MEET EEE UNE TE A DENE WE SA A = ESR a ET
The fundamental constants of a camera may be expressed by listing
the external angles of entry 9 against the measures on the plate to
which they apply. This is the basis of all camera calibration. Why
is it then that these measures are not listed on the calibration
certificate?
The usual practice is to state on the calibration certificate a
value for the principal distance against a list of distortions corres-
ponding to various angular distances from a point of origin. These
are not basic measures at all. They are obtained from the original
measures by a mathematical process involving various adjustments,
distributions, interpolations and weightings. It is well known that
these distortions may be expressed in a large variety of different
Ways. Furthermore, the distortions are 4 given in the form of a
graph in which the number of observations made and the degree of inter-
polation employed is effectively hidden.
an
The writer believes that the analysis of the basic measures should
be undertaken by the photogrammetrist using a method which suits best
his own purposes, and that there is no need for the analysis of these
measures to be undertaken by the calibrating authority. If this
principle was adopted it would altogether absolve the calibrating
Sa from the necessity of explaining his computing techniques.
Under present practice if he does not do this in sufficient detail it
is impossible for the photogrammetrist to work back from the data
supplied to determine correctly the original observations. These it
is essential for him to know if he wishes to determine his own
distortions by & method most si uit: ble for the task he has in mind.
The writer therefore advocates that whatever information is
]43 E3 nt PA nada +he nas mescirae nf + and Q
provided on a calibration certificate, the basic measures of x and ©
si ) Ex ] ] 1 rs 1 C inc lu led.
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