ANALYTICAL AIR TRIANGULATION MADE MORE PRACTICABLE
(Some Recent Progress in the Design of Machinery Suitable for Analytical
Air Triangulation and its Possible Impact on the Practice and Development
of Air Survey)
by A. M. Wasser,
The Survey of Egypt, Giza, Egypt.
Paper presented to the Seventh International
Congress of Photogrammetry. Washington, D.C., 1952
1. The Place of the Analytical Approach.
To claim that analytical methods will replace the use of plotting machines in
air triangulation would be just as unwise as to maintain that the work can be done
as accurately using plotting machines as by analytical methods. It may however
be safe enough to forecast a much wider application of analytical methods of air
triangulation in the near future. Much work is in fact being carried out at present
time in the United Kingdom by the Ordnance Survey.
Dislike to calculations is common and, I think, natural. Dr. Krames reminded
us in the last Congress of Prof. Schwidefsky's definition of photogrammetry as the
'art of avoiding calculations. That the plotting machine has achieved this in
connection with detail plotting and contouring is of course undisputable. But has
it fulfilled this objective in air triangulation? I think not. A comparison between
the early methods of air triangulation using plotting machines and the modern
versions ?? substantiates the contention that the use of the plotting machine alone
has not been entirely successful, and that it needed to be supplemented by a con-
siderable amount of calculations. In fact, what contrasts the old and new methods
of triangulation using plotting machines is the amount of supplementary comput-
ational work in the latter. This injection of the practically non-computational
method of the late Prof. von Gruber by a steadily increasing volume of calculations
has been forced by the lack of success of the all-machine method in practice.
The instrumental errors of the machine are not the only or even the most
important source of inefficiency. The larger proportion of the blame rests on the
photography; but, while improved photography should be urged, the fact remains
that we cannot wait for it. In other words, we have to obtain the best out of
whatever photographs we are given. The point is that in order to correct for al!
the instrumental and photographic errors one would have to use an expensive
plotting machine almost for the sole purpose of measuring rectangular coordinates
— a job which can be well done by means of the much cheaper stereocomparator.
For example, the use of a reseau ") ruled on the register glass on cameras built
on this principle, as developed by the Ordnance Survey “’, should help reduce the
*) an array of fine crosses.
