-9- 
Regrettably, this promising system obviously did not fulfil the expec 
tations, since no further developments are known. 
Tests resulted in an accuracy of 5° (standard deviation). 
On the other hand, the development of an inertial platform, keeping the 
survey camera vertical to + 1° has been published in the U.S. This is a 
component of the ANQ.-28 system and although this appears to be the ultimate 
solution to one of the photogrammetric problems, this special equipment is 
extremely heavy and expensive and requires the use of a special aircraft. 
It is therefore obviously out of reach for the average photogrammetric 
organisation. 
The author wonders whether such a highly developed system is really required 
for general photogrammetric purposes. An inertial system which only 
registers the deviation of the camera tilts, without controlling them by 
servo mechanisms would probably suffice. 
Furthermore, it would be sufficient to register the tilt deviations with 
respect to any fixed axis system in space instead of the true vertical. 
Certain changes in this reference system would be permissible as long as 
they are sufficiently linear or otherwise predictable within short time 
periods, such as an hour, as they could be accounted for in the computa 
tional stage. 
Inertial system designers are therefore kindly, but most urgently requested 
to re-examine their specifications and to supply civilian agencies with 
equipment, compatible with the normally available aircrafts and funds. 
Provisional specifications for such a system might be as follows: 
1) Digital or optical registration of the rotation of the camera system with 
reference to an inertial system. 
2) Accuracy 1-2° (standard deviation). 
3) Linear and other regular or predictable changes of the inertial system 
are permitted during normal flight periods of about an hour, since their 
magnitude can be derived by interpolation from the photogrammetric data. 
4) The absolute orientation of the inertial system need not be known, as it 
can be derived indirectly from the photogrammetric system. 
Such a system would, together with the possibilities of Laser APR, certainly 
have a tremendous influence on the attainable results of aerial triangula 
tion. 
Hiran, Shiran, Aerodist 
These instruments allow the determination of the distance of the aircraft 
from similarity equipped ground stations. The plan co-ordinates of each 
exposure station can be computed by trilatération, provided that there is