WM. (D Qo
~~ Te Vv (VY
t X U
3
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
