2 
the same as that of the radio distance recorder and the hyperbolie position finder. 
In the radio distance-recorder method the master station is airborne, while the two slave 
stations are located at points on the ground whose geodetie coordinates are known. In the 
hyperbolie position finder method the master station and two slave stations are on the 
ground, and the fourth is airborne. The changes in phase-difference cycles caused by the 
plane proceeding on its course are recorded photographically. If the radio distance 
recorder is made use of, the changes in the distances from the master station to either 
of the slave stations can thus be obtained. In case the hyperbolic position finder method 
is employed, the changes in the number of cycles correspond to the changes occurring 
in the differences of the distances between the airborne station and the master station 
and also from the former to one of the slave stations on the ground. Therefore, to find 
out the distances from the airborne station to those on the ground the initial recording of 
the number of cycles is made over an area where ground control is provided. The geodetic 
coordinates of the first camera station can then be obtained photogrammetrically from 
the initial photographs, and the distances from it to the ground stations computed. 
After these have been obtained, and since the increments of the distances or the increments 
of the differences of distances are known, the distances from the ground stations to any 
camera station position may be computed and its co-ordinates found. The range of the 
radiogeodetic stations is about 350 kilometres, the wavelength of the transmitting station 
being in the neighbourhood of 220 m. The ratios of retransmitting by the slave stations 
are ?/, and ?/, of the carrier frequency. The mean square error in camera station 
positioning is about 5 metres, its greatest value is 15 metres. 
The gyro-stabilizing equipment is a motor driven gyroframe with a pair of two- 
step gyroscopes, each of these stabilizing the serial camera about one of the horizontal 
axes. An electrolythic level is provided for correcting the gyros. The rate of correction 
is varied: to bring the camera speedily to a specified position the rate of correction is 
made to be about 5 minutes of arc per one second of time; in the course of work the 
rate is changed to approximately 0.8’ per sec. The mean square value of tilt in photo- 
graphs taken with the aid of gyro-stabilizing devices is about — 10', the maximum being 
around 40'. The main source of errors in the performance of gyrostabilizing equipment 
is the effect of linear accelerations mostly due to long-period vibrations of the aircraft. 
There is no doubt whatever that the present accuracy in recording the elements of 
absolute orientation of photographs is far from adequate from the point of view of 
producing topographic maps by photogrammetric means; so research is carried on in the 
USSR with a view to improving the accuracy of positioning. However, even the results 
available at present make it possible to increase the accuracy of photogrammetric pro- 
cesses, reduce the amount of ground control, and simplify some aspects of office work. 
Two techniques are employed at present in using the elements of absoluteorientation 
obtained during the flight. One is to use the data directly, after proper checking; the other 
involves simultaneous adjustment of those quantities and of the values determined 
photogrammetrically. Obviously, the higher the degree of accuracy in recording the 
elements of absolute orientation, or the smaller the scale of the map to be produced, 
the more reasonable it will be to take recourse to the first method. On the other hand, 
if the photogrammetric measurements are performed with a high degree of precision and 
the map to be produced must be of a higher standard of accuracy, while the errors in 
recording are rather great, then, of course, the second method should be considered 
preferable. 
For making topographic maps on the 1: 100,000 scale the cameras are mounted 
in a gyrostabilizing device, the statoscope and radioaltimeter readings being recorded 
at the moment of exposure. Cameras used have 55 mm or 70 mm focal lengths, the scales 
are 1: 70,000—100,000. The fore-and-aft overlap is 60 per cent; the side lap, 30 per cent. 
Apart from the main strips necessary for covering the whole area to be mapped, control