ning process, and the horizontal parallaxes follow a
simple, linear function of the terrain elevation diffe-
rences. As a result, stereoscopic viewing is particul-
arly simple and convenient, and the vertical diffe-
rences in the “stereomodel” can be determined at any
point with great ease. It is obvious that stereo-ortho-
photos, complemented of course by contours, offer an
advanced concept in the presentation of terrain [6]
and at the same time, are very suitable for converting
orthophoto maps into line-drawn maps, if this should
be required.
There is a great advantage in this approach as
far as conventional map production is concerned,
which seems to be particularly valid for less deve-
loped areas: The basic map manuscripts are produced
with great rapidity in a simple semi-automatic scan-
ning process, and the actual line-drawing and sym-
bolization are removed to the stage of final drafting
where they more appropriately belong.
The principles sketched above have been experi-
mentally tested in our laboratories. The purpose of
discussing them here is simply to indicate that the
orthophoto technique is only in its infancy and that
its various possibilities greatly exceed the initial "map
substitute" concept. Although at the moment small-
scale mapping may not be the field in which this
technique will have the most obvious application, I
feel that these thoughts on the subject are important
enough to be given thorough consideration.
Super-wide-angle photographs
The impact of super-wide-angle photography on
photogrammetric operations was initially not as great
as one expected or hoped for. The reason may be
twofold: initial instrumental difficulties in plotting
and secondly, somewhat inferior definition of super-
wide-angle photographs. The super-wide-angle lenses
were developed before plotters that could accept su-
per-wide-angle diapositives of original size were avail-
able. This of course delayed the acceptance of super-
wide-angle photographs in many standard topogra-
phical mapping operations. But, analytical aerial tri-
angulation and availability of moderately priced de-
tail plotters that can accept original size wide-angle
photographs, removed this difficulty. However, the
stimulating effect of the initial development was some-
what lost. It is also probable that in the meantime
many agencies have acquired plotters not necessarily
tailored for use of super-wide-angle photographs.
'This development, if my analysis of the situation
is correct, is rather unfortunate in view of the defini-
tely superior accuracy obtainable from super-wide-
angle photographs as a result of larger base to flying
height ratio [8], and other important technical and
economic advantages. One of these advantages is the
ability to reduce the level of the flight which makes
it significantly less expensive. Particularly in map-
ping projects of less developed areas, use of super-
wide-angle photographs should result in overall im-
proved efficiency and reduction of costs.
Colour Photographs
With the rapidly growing use of aerial photo-
graphs in various disciplines, mainly for photo-inter-
is steadily increasing. This trend is understandable.
A further increase of interest in this direction should
be expected, particularly since it is likely that colour
orthophoto maps will provide an additional incentive.
Photogrammetric Engineering and The Photogram-
metric Record relatively recently published some in-
teresting articles on the subject. Instead of repeating
various arguments for the use of colour aerial photo-
graphs, I would like to record the fact, that the main
difficulty in using colour photographs lies in the in-
terphase operation: production of colour glass dia-
positives is not mastered yet and the diapositives
consisting of the colour film transparency glued to a
pretation purposes, the interest in colour photographs
glass plate occasionally produced are prohibitively
expensive. It is also true, that the results from colour
photographs are somewhat worse, as far as accuracy
is concerned, than the ones from usual black-white
photographs. There is little information on this sub-
ject and, therefore, I am including our own results
obtained from experimental flights over a very precise
test area. (See below.)
A more vocal interest on the part of photogram-
metrists in the use of colour photographs could per-
haps prompt the photographic industry to solve the
question of colour diapositives and thus master one
of the main difficulties in using colour photographs.
NRC — Monocomparator
Film Diapositives Standard error Number Total
in photoscale of Number
Models of Points
mx my mz
a Panchromatic black-white, 5u 6u 10u 22 906
estar base glass
b Kodak Ektachrome MS, black-white, 7u Tu 154 10 333
estar base glass
c colour, 7u 9u 13u 8 117
on glass
Difference in accuracy between a and c. 40 96 44 96 30 96
