\Z are 
rial photo. 
photo using 
hen ps and 
help of the 
rectificated 
shift vector 
ctor S is to 
— AZ) 
Zz 
— AZ ;(3) 
be equal to 
limits. For 
the scale of 
or period T 
.1 and R2 
] in basic 
has to be 
on the L1 
ained during 
value of the 
ing for the 
que is the 
in the plane 
differs from 
escribed by 
(4) 
| photogram. 
is less than 
exceed 1096 
e calculated 
the help of 
  
spatial coordinates of the points on the glacier 
surface. 
It is necessary to note once more common positive 
quality of the pseudo-parallax method: to identify 
the points on the stereopair photograms needs no 
their accordance to definite contours. The point 
positioning, both movable and stable, is defined by 
its coordinates on the L1  photogram, and 
comparison with positioning on the R2 photogram is 
done by stereoscopic sighting on stereomodel L1- 
R2 surface. When the glacier points are moveable 
this surface is pseudo-surface. 
Conducted works and used equipment 
Photos of Medvezhy Glacier (Fig.2) were made 
from repeated aerial surveying along the glacier 
lengthwise axis with time intervals from several 
days to several weeks. When repeated aerial 
surveyings were made, definite requirements as 
regards for aerial surveying strip direction, 
photography height and time were set. Said 
parameters have to be as similar as is possible for 
different aerial surveyings. Used aerial camera has 
a 200 mm focal length, 180x180 mm frame 
dimension and a 1:20000 average photography 
scale. 
Fig.2. Fragment of the aerial photo of the main 
icefall of the Glacier "Medvezhy" in the scale of 
1:14000. The photo central area is shown. 
  
301 
To digitize data by Desk Jet 3c Scanner with 600 
dots/inch resolution contact  photoprints from 
negatives were used. Because of significant 
deformation of the photoprints it is necessary to 
carry out detection and allowing for deformation 
during preliminary processing and to minimize its 
effect on the results. Two methods of deformation 
detection and allowing for were tested: with the 
help of fiducial marks on the photos and with the 
help of the crosses on the flattening glass of the 
aerial camera. 
The first method is based upon off-line conversion 
of the photogram points. Coefficients of conversion 
are calculated with the help of fiducial marks 
measurements. This method is often recommended 
in literature when scanned imagery is measured 
(Fryer, 1993). The second method is based on the 
crosses measurement and corrections calculation 
with the use of the 2nd degree polynom. 
Practice has shown that the first method lowers 
deformation to values of 2-3 pixels, the second one 
- to 1 pixel. This magnitude (0.04 mm in our case) 
may be considered as real accuracy of contact print 
measurements. Experimental estimation of obtained 
vectors accuracy has confirmed that fact. Such 
accuracy is able to solve different tasks taking place 
in application of measurements of aerial 
photograms. Therefore, it may be stated that 
scanning with a resolution more than 600 dots/inch 
is not reasonable because improved resolution 
could not be realized due to effect of residual errors 
of the photograms. 
Measurements were carried out on IBM PC 486 
equipped with stereoscopic spectacles on liquid 
crystals with 100 cycles per second working as a 
shutter. Design of the spectacles and their software 
for synchronized working with PC belongs to IBIK 
firm. Such a system provides for maximal use of 
the display area and has been tested for PC 
operations. As an example, publication (Nobuhico, 
1992), may be mentioned. All stereoscopic 
measurements are carried out according to 
stereocomparator technique. 
Software and forms of data representation 
Software which. has been developed in the 
Laboratory of Aerospace Methods enables us to 
provide stereoscopic measurements allowing for the 
photogram deformations, in order to reconstruct 
models using simultaneous and different time 
photograms, to calculate coordinates and shift of 
the movable point, to represent velocities field 
cartographically by vectors (Fig. 3) and by the newly 
developed graphical method, so called "strezhinel" 
lines. These lines (créated from Russian word 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996