ANALYTICAL PHOTOGRAMMETRIC INSTRUMENTS 
8 
graphic target image registration is an addi 
tional feature that makes the instrument 
attractive for practical use. 
The measured coordinates cannot be read 
directly on the instrument. They are auto 
matically recorded as 6-digit numbers, with 
2u as the least count, together with a 4-digit 
point number, and 4 additional auxiliary in 
dexes. The data can be recorded on punched 
tape or punched cards. In addition, the same 
information is recorded by a typewriter 
which can, through the use of tape reader, in 
sert clear text for desired headings. 
As an added feature, the manufacturer has 
provided a small electronic computer which, 
if used as on-line equipment for spatial trian 
gulation computations, converts the Stecom- 
eter equipment into a complete photo- 
grammetric data evaluation system. This is 
an interesting experiment. Its justification 
will depend again on economical considera 
tions. The full benefit of the ±2u measuring 
accuracy of the instrument can be obtained 
only with rather sophisticated mathematical 
models, which are clearly out of the range of a 
small computer. One concludes from Dr. 
Weibrecht's discussion that the Stecometer 
itself, with automatic registration, has the 
potential to provide raw data which can 
satisfy quite stringent accuracy requirements 
in aerial photogrammetry. In combination 
with a small on-line computer, its potential 
is attractive for problems which can tolerate 
some degradation in the execution of the tri 
angulation problem, or where the use of less 
than optimum raw data does not demand the 
full potential of analytical photogrammetry. 
Mr. Blachut’s paper is also concerned with 
the problem of devising an economical nu 
merical evaluation system. The author, while 
recognizing the basic necessity for stereo 
scopic identification in topographic applica 
tion, reiterates the praxis-proven fact that an 
independently-executed marking or point 
pricking operation is feasible when the ex 
pected overall accuracy of measurement is 
±5 to ±10 microns. The measuring of the 
pricked point itself then introduces only a 
minor degradation which can be accepted 
without reservation. In addition, there is a 
broadening field of photogrammetric applica 
tion where the mono-plate reduction idea is 
quite feasible. 
Realizing the need for an optimum tool, a 
precise and low-priced mono-comparator, 
based on an idea by Mr. Helava, was devel 
oped and produced by the Applied Physics 
Division at the National Research Council in 
Ottawa, Canada. The instrument was de 
scribed in detail by Mr. Smialowski at the 
Second International Photogrammetric Con 
ference in Ottawa. A novel feature of this in 
strument is a multi-measuring mark system 
which allows for a very simple optical train. 
This feature obviously limits the instrument 
to one type of measuring mark, which is 
justifiable, however, in the case of pricked 
points, or for the measurement of imagery 
which has a definite and predictable size 
and shape which is compatible with the 
measuring mark. 
The measured coordinates are recorded 
automatically by using a shaft position-en 
coding device. Visual reading by means of 
drums is also possible. 
Mr. Blachut discusses the old problem, 
which is still with us, of the need for a pricking 
device which assures marks that are suffi 
ciently circular so as not to impair the sig 
nificance of the pricked location. 
The application of the mono-plate prin 
ciple in numerical photogrammetry is seen by 
Mr. Blachut as being especially suitable for 
photogrammetrists and surveyors who can 
not afford an expensive stereo instrument, for 
universities and other teaching organizations, 
and particularly for various physical, engi 
neering and industrial laboratories. 
The rest of the paper is devoted to a 
comparison of accuracy when employing a 
Wild A-7 in its conventional mode and as a 
mono-comparator. The raw material was used 
both without marking, and with drill hole 
marks made on a Wild PUG. 
The final results do not differ significantly 
in accuracy. Consequently, no valid conclu 
sions can be drawn about the various opera 
tional arrangements. It appears that the error 
inherent in the raw data overshadows the 
influence of the specific measuring procedures. 
The mean error of unit weight at image scale 
is about ± 10/x. The lack of conclusive results 
points out that tests of this nature—especially 
if conducted on an interagency basis, or as 
international experiments—should be based 
on high-quality raw data in order to be con 
clusive. On the other hand, the results accen 
tuate the fact that it takes, in praxis, con 
siderable precaution in all operational steps