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Investigations have shown the possibility of using 
aerial photographs for the purpose of correctly observing 
erosive features of relief. By comparative analysis of 
aerial photographs taken at different periods of time,it 
is possible to bring to light dynamics and natural deve- 
lopment of phenomena. 
‘At the present time, in connection with certain 
scientific and engineering problems, the method of 
dynamic (four-dimensional) photogrammetry which is now 
being put into practice of particular importance is; 
in this method, in addition to the usual values X,Y,Z, 
the t-value (time) is measured. 
For instance, the dynamic triangulation can be 
applied for solving such problems as determination of . 
speeds and trajectories of moving objects. To this aim 
spatial coordinates of points at the exposure moment are 0 1 e 
found and approximated by curves. In this way, the dyna- > 
mic photogrammetry establishes a connection link between 
the image of an object on a photograph and the natural 
parameters of its movement (aerial surveying of flows, 
filming of deformations of tire-covers, vibrating de- 
tails etc.). 
When carrying out determinations of Stream-speeds 
in water reservoirs on the base of aerial photography 
(taken from helicopters with the help of a radioalti- 
meter),- photographic images of blocks of ice, shields, 
artificial coloured marks etc. are used as "marking 
objects". As & result of plotting a location plan of the 
marking objects at the moments of exposure is obtained. 
The speed of current is computed on the base of distance 
and time intervals between successive exposures. 
In the four-dimensional terrestrial photogrammetry 
both the graphic and analytical methods of coordinates 6 ® 
determination are applied. 
The principles of determining the spatial coordi- 
nates X,Y,Z of an object are similar, irrespective of 
the object being in movement or at rest.