6 
PHOTOGRAMMETRIC ENGINEERING 
a system whose sole aim is to facilitate their 
recovery, and they are then measured in a 
simple monocomparator, preferably one 
which is provided with a reticle which permits 
pointing by framing. It is certain that this 
procedure is particularly economical; it is also 
quite fast since point selection and point 
measuring are not separated. It does not 
eliminate the need to choose and mark the 
images that will be used, but this preparation 
is common to all the methods; at the most, 
one can say that the points should be par 
ticularly minute. 
According to the articles published by the 
D.O.S., the results of preliminary trials are 
very satisfactory: if they are verified, they 
will have made a serious and almost sacrile 
gious attack on the fundamental principle of 
stereophotogrammetry which says that only 
by stereoscopic fusion is it possible to assure 
the correct identification of corresponding 
points that are not targeted on the ground, 
with a precision that is considered axiomati- 
cally to be higher than that of monocular 
pointing. There is room for apprehension, 
however, that the points whose coordinates 
will be measured in the vicinity of the center 
of more or less ill-defined spots, and which can 
appear very different on different photo 
graphs, may not be exactly homologous; but 
it is possible that, because of the small dimen 
sions of the spots, the error thus committed 
will be on the order of a few microns and can 
be considered negligible. 
Great hope has been placed on automation 
of procedures for selecting the points, and for 
stereoscopic pointing, by use of diapositive 
image correlators. But these image correlators 
make only a relatively gross simulation of 
stereoscopic fusion, and one cannot hope for 
very much saving of time, since the coarse 
matching would, without doubt, have to be 
done manually. Besides the fact that the 
equipment used in this work would be very 
costly, the use of this equipment would not 
eliminate the tedious work of preparation, 
with the many manipulations of the plates 
that would be required. 
An entirely automatic solution, sometime 
in the future, can nevertheless be envisioned; 
it would consist of reducing all the photo 
graphs to digital form, using a technique that 
has already been tested: each photograph is 
broken down into very small elements and 
their photographic densities are recorded ac 
cording to a scale composed of a number of 
gradations, the analysis of density being 
made, of course, automatically, by scanning, 
with the aid of, e.g., an IBM analogue scan 
ner. Starting with these data, recorded on 
magnetic tapes, disks, or some other medium, 
it would be theoretically possible to resolve 
all the problems of aerotriangulation. Per 
haps we will be set free from the idea of dis 
creet points, the calculations being hence 
forth concerned with finite areas, and ending 
in the definition of complete topographic 
surfaces, broken down into elements dx, dy, 
by knowing the elevation and the photo 
graphic density of each element, irom which 
one could obtain orthophotomaps with con 
tours directly. Thus, there would be realized, 
at the same time as complete automation, the 
synthesis of aerotriangulation and of plot 
ting; but it is hardly necessary to state that 
this will not take place tomorrow, nor before 
the next Congress of the ISP. 
References 
Thompson, E. H., 1965, Analytical aerotriangula 
tion: Bulletin de la Société Française de Photo- 
grammétrie, no. 18, p. 3-8. 
Inghilleri, G., and Galetto, R., 1967, Further 
developments of the method of aerotriangula 
tion by independent models: Photogrammetria, 
v. 22, no. 1, p. 13-18. 
Karara, H. M., 1967, Mono versus stereo analytical 
photogrammetry; theoretical considerations and 
experimental results: Photogrammetria, v. 22, no. 
3, p. 99-113. 
Eden, J. A., 1967, A new fast working approach to 
analytical photogrammetry: The Photogram- 
metric Record, v. 5, no. 30, p. 474-491.