Letters to the Editor
| Date | 01 July 1963 |
| Author | J. D. Moreland |
| Published date | 01 July 1963 |
| DOI | 10.1177/0032258X6303600709 |
| Subject Matter | Letters to the Editor |
Letters
to
tbe
Editor
PHOTOGRAPHING
ACCIDENT SITES
DEAR
SIR,
Sergeant Blair has raised some important points in his letter. I
agree that the major advantages of a helicopter survey are its poten-
tial speed and the facility with which both large and small areas
could be photographed. Against these must be weighed, however,
its relatively high capital and running costs. To a certain extent the
two survey methods are complementary; ours is suited to small
urban districts while the other appears adapted to larger rural areas.
It
should be realized that the camera/mast assembly developed at
the Road Research Laboratory is a prototype. The survey time
could behalved quite readily and if the system was adapted to a high-
speed estate car it should be suitable for work on motorways.
Photography "adequate for production as evidence in court proceed-
ings"
is not a simple matter. There are several sources
of
error in
aphotographic survey and these must be known before the accuracy
of measurements taken from a photograph can be stated.
If
correct
photogrammetric procedures are used then many
of
these errors can
be controlled and reduced to a point where, for the purposes of
accident reconstruction, they may be neglected.
There is one source
of
error over which there is no control and
which may lead to difficulties in photo-interpretation unless special
precautions are taken. Differences in height between objects result
in differences in their plan position. The effect is zero at the centre
and maximum at the corners of a vertical photograph. Vertical
objects appear to radiate from the centre giving the picture its vertical
perspective. See, for example, the standing spectators in Fig. 4
of
our paper. While such obvious differences in height lead to an easy
interpretation, the same effect may appear more subtly. In the same
photograph a private car appears, at first sight, to be deeply imbedded
in the side
of
a trailer. This appearance is due to the difference in
height between the car and the load on the trailer.
If
the outlines of
the car and the trailer (the near end of which is visible) are drawn it
will be seen that the degree
of
engagement is far less than it appeared.
It
is this kind of situation, where an expert and a layman could
differ markedly in interpretation, which could give rise to difficulties
in court proceedings.
Yours faithfully,
J.
D. MORELAND
359 July 1963
To continue reading
Request your trial