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strips at right angles to them with 80 per cent fore-and-aft overlap are flown every 
80—100 kilometres. These latter are flown whenever radioaltimeter and statoscope data, 
or radiogeodetic station data, are recorded. Ground control consists of horizontal positions 
of ground stations and of a few points in their vicinity for obtaining the coordinates of 
the camera station on the initial photograph. In addition, on control (transverse) flights, 
at intervals of 50—60 kilometres, four spot heights are determined within an overlap. 
When the coordinates of the camera station on the first photograph have been 
found, which is done on one of the universal stereophotogrammetric instruments, the 
sloping distances from this point to the slave stations are computed. From the increments 
of cycles the increments of distances and the distances from any camera stations to the 
ground stations are found. These sloping distances are transferred on to the spheroid, 
after which geodetic horizontal coordinates are found for every camera station on the 
photographs of the transverse strip. Analytical control extension is performed on the 
multiplex (for mountainous regions) or by means of photo poligonometry (when the 
country is flat), the use of radar altimeter records being obligatory as it greatly lowers 
the rate in which longitudinal errors of a photogrammetric chain increase. 
Radar altimeter and statoscope data enable the heights of all nadir points to be 
determined separately for every main and transverse strip, all these elevations being 
referred to the plumb point of the initial photograph in every strip. By the use of ground 
spot heights on the transverse strip photographs, elevations of the nadir points of those 
photos are determined, following which the nadir points of all the other photographs 
both in the main and the transverse strips are found. 
The extension of vertical control from the main strips is carried out on the 
multiplex (for mountainous regions) or by the differential method of spatial triangulation 
as well as by making use of the Undistorted Stereomodel technique and bridging on the 
stereometer (for flat territories). Absolute orientation and adjustment are based on the 
elevations of the nadir points both in the main and transverse strips. 
As to the rest of the processes involved, these do not undergo any alterations; 
however, owing to lesser tilts in the photos, they become considerably simplified. In 
producing 1 : 25,000—1 : 50,000 maps it is sufficient to determine horizontal positions by 
radiogeodetic means, and vertical positions with the aid of the radar altimeter and the 
statoscope, provided the contour interval is 5 metres and the permissible mean square 
error is — 1.7 m. However, whenever this is the case, it seems advisable to have the photo- 
grammetric and the radio data adjusted simultaneously. According to the type of the 
country, the aerial cameras used are of different angles, from f, — 55 mm/25 — 130^ 
— for the plains — up to à = 200 mm/26 = 60° — for alpine regions. The specification 
for the fore-and-aft overlap is 80 per cent to provide for two independent vertical 
control bridging processes. Transverse strips should be flown every 50 kilometres, to 
produce closed circuits of radiogeodetic data. The data provided by the radiogeodetic 
stations, as well as those furnished by the radio-altimeter and the statoscope are recorded 
both on the main and the transverse flights. Horizontal ground control comprises ground 
stations’ positions but in this case the hyperbolic position fixing is not to be employed 
because of its inferior accuracy; besides, the range of the stations does not exceed 
250 kilometres. 
To provide for the proper checks in the areas farthest from the ground stations, 
horizontal positions of two more points are determined. Just as in 1 : 100,000 mapping, the 
horizontal positions of a few points in the neighbourhood of the ground stations are 
determined for the sake of obtaining the initial photograph nadir point coordinates. 
Ground control elevations are found of four points per overlap over intervals of 10—12 
exposures along every strip. 
Later on horizontal positions of nadir points of main and transverse strips are 
determined, the coordinates inside every circuit are adjusted and photogrammetric hori- 
RON EIER OUT