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1) Obtaining the coordinates. 
2) Photo triangular spreading net of ground control 
points. 
3) Aerial photos external orientation. 
4) DTM production. 
5) Aerial photos projection on DTM, contours 
identification. 
From mathematical point of view, stages 2 through 4 
are an integral process which essence consists of 
establishing correlation and calculation parallax in 
stereopairs, only may be done in sequentially stereopair 
by stereopair, that inevitably accumulates 
geopositioning error as the distance increases from the 
true, geodetic specified ground control points. 
Plus, nothing is principally changed in terms of resulting 
accuracy, with usage of automatic correlation methods 
for mutual photos orientation, instead of manual, as well 
as DTM production with digital photogrammetry 
systems instead of relief depicting via visual stereo 
measurements. 
Another issue is utilizing GPS receivers in aerial 
surveys for registration of principal point spatial 
coordinates. Availability of such data, though 
significantly improving the situation (due to reduction of 
stereomodel mobility during spatial orientation), 
nevertheless can not be deemed sufficient for full 
automation of stereotopography process. 
2) The second category of problems consists of variety 
of well known particular limitations of 
stereophotogrammetry method. These are studied in 
detail therefore it is no sense in thorough description 
here. Let us just mention the following. 
The problems of such nature are quite diverse in their 
characters, but they all are in general tied with issue of 
points correlation on stereopair. In certain cases this 
leads to complete inapplicability of the method, for 
instance in snowed or sanded landscapes with a full 
absence of visual texture. In other cases this problem 
puts the results' quality in dependence on the number 
of factors like average forest elevation and density 
when surveying forestry, or buildings shape when 
mapping city landscapes. 
Limitation of stereophotogrammetry method emerges 
mostly in the most practically meaning applications 
connected with survey of complex and full of objects 
scenes. Particularly due to this reason, large-scale 
mapping of city landscapes with significant share of 
multilevel buildings can not be done by exclusively 
aerial survey methods, thus forcing massive 
involvement for this goal carrying out of on-ground 
topographic survey, extremely expensive in city 
conditions. Besides, there are season limitations 
restricting aerial surveys in presence of significant snow 
cover or vegetation with leaves. For most part of the 
Russian Federation such limitations only leave 1.5-2 
months a year for aerial survey. 
Practically, such problems often lead to the serious 
deformation of technology that causes doubts about 
results correctness. Thus, production of DTM of a big 
city area considered as compulsory within 
stereotopography method, is deemed such a labor 
consuming and expensive task affecting the overall cost 
of project that a 'compromise' is offered to use a relief 
model taken from existing topographic map of 
appropriate scale. Given the extremely low metrologic 
quality of existing topography basis in Russia, it is only 
left to guess what consequences in future would be 
caused by such decisions when doing, for example, a 
cadastre system to regulate real estate relations. 
2. METHODIC PROBLEMS OF JOINT APPLICATION 
OF LASER LOCATOR AND PHOTO DATA 
Advantages of laser locator methods in DTM production 
are commonly recognized. 
However, this does not limit the meaning of laser 
location in topography. Consistent development of idea 
of combination laser locator and digital photo aerial 
survey data makes it reasonable to hope on almost fully 
automatic technology of aerial survey data processing 
for topographic material production. 
2.1. Digital Terrain Model 
DTM itself obtained with laser location method, has a 
number of obvious advantages comparing with classical 
stereophotogrammetric DTM: 
♦ Traditionally the accuracy of absolute georeferencing 
on WGS-84 spheroid is considered as a main 
advantage. 
Laser scanners (locators) manufacturers usually 
declare an accuracy of 15-30 cm on geodetic elevation. 
This value is generally determined by achievable 
accuracy of range signal measurement with appropriate 
electronic unit. Guaranteed planimetric accuracy is 
specified in proportion to survey altitude, and normally 
ranges from 1/1000 to 1/2000 of flight altitude, that 
refers to value of 25-50 cm for typical altitude of 500 m. 
It is clear that above values satisfy accuracy 
requirements for the most large-scale topographic 
maps. It should be mentioned, however, that these 
evaluations are not unconditioned, and only achievable 
in the most favorable survey conditions. 
Such accuracy of georeferencing can not be achieved 
with any other remote sensing equipment. This 
determines a major difficulty in attempt of experimental 
verification - practically the only way of such verification 
is low-productive differential GPS on-ground 
measurements.