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resolution dropped to the level of 75% at the centre, 
and to 90% at the edges of the original camera 
resolution. For the wide angle Flectogon 4/50 at the 
relative aperture 1:4 the image resolution without 
the reseau-glass was 37 lines at the centre of the 
field of view and 10.5 I/mm at the edges. The 
glass-plate caused the resolution drop by 8.7 l/mm 
at the centre and by 0.6 l/mm at the edges. Relatively 
resolution dropped to the level of 76% at the centre 
and 94% at the edges comparing with the original 
camera resolution (without the 1.6mm reseau glass 
plate). 
4. GEOMETRY OF PICTURES TAKEN WITH 
THE ADAPTED RESEAU CAMERA 
4. The reseau transformation accuracy 
The first, very important step of processing of 
photographs takea with a reseau camera, it is 
elimination of systematic errors appearing during 
image recording on the film. These systematic errors 
are due to the film differential shrinkage, film non- 
flattness in the moment of exposure, and by recording 
of the image slightly out of the plane of fiducial 
frame. The elimination, or at least reduction of 
those systematic errors can be achieved by trans- 
formation of photo-coordinates onto the reseau fidu- 
cial frame. The transformation coefficients can be 
calculated by fitting the coordinates of reseau-crosses 
surveyed on the photograph onto the coordinates 
of crosses of reseau master pattern surveyed directly 
on the reseau plate (the reseau master pattern was 
surveyed with the accuracy +0.8um using Zeiss Jena 
Ascorecord). 
In the presented experiment we have examined 12 
photographs taken with our 6X6 reseau camera, to 
get answer to the following questions: 
e by what value of deformation are influenced the 
photographs, 
e which type of transformations would be the best 
for photo-coordinates refinement, 
e how the number and distribution of the reseau 
active crosses influences the accuracy of refine- 
ment procedure (as an active reseau cross is 
meant such a czoss of the reseau pattern which 
is actually used as a control point in the coor- 
dinate refinement procedure). 
To get answer to the above questions the experimental 
12 photographs selected from three films (ORWO NP 
20) have been measured. On each photograph there 
should be registered 49 reseau crosses, but on a few 
pictures one cross could be omitted if imaged on the 
black image fragment and badly visible, and such 
picture could be partially excluded from the analysis. 
The reseau crosses were surveyed with the accuracy 
+2um using the Zeiss - Jena Stecometer. The infor- 
mation about the size of errors caused by the above 
described deformations can be achieved by isometric 
transformation of coordinates of all the 49 crosses of 
the photograph onto the coordinates of all the 49 
crosses of the reseau master pattern. The residual 
deviations on all this active points will describe optimally 
the quality of the identity of the both compared sets 
of points, as the isometric transformation does not 
change size or shape of the transformed picture. The 
results of this isometric transformations shows the 
average standard error calculated for the 12 experimen- 
tal frames is +36.3um. The analysis of errors shows 
that the residual deformations fluctuate up to 50% of 
average standard deviation even for pictures recorded 
within one piece of film. There was found experimentally 
that the best description of deformations give: bilinear 
transformation and projective transformation. Compar- 
ing the results of those two transformations when 
applied to our test photographs it was noticed that 
the average standard deviations are in both cases 
identical avr. mx=*24um, avr. my=*27um, avr. 
mp = +3.7um. However, the bilinear transformation is 
less sensitive to noises and can be used to describe 
the photograph deformations. To check the property 
of the deformation there were calculated separately 
the bilinear transformations for the points distributed 
over the area of each quarter of the frame. The 
calculations ranged over only those quarters of each 
of the 12 experimental photographs on which there 
was possible to measure all the 16 reseau crosses (all 
the 16 crosses were active in the transformation). The 
calculation results are shown in table 1. And below 
are the average values of standard deviations, and their 
errors, for the separate quarters: 
— for the I quarter avr.mp=*19um, o==0.4um, 
— for the II quarter avr.mp — €£2.3um, g— x 0.6um, 
— for the III quarter avr.mp = t1.8um, g — x0.3um, 
— for the IV quarter avr.mp ^ £3.1um, g — x0.4um. 
The results show that the average value of standard 
deviations taken from the separate transformation of each 
quarter is smaller than the one for the full frame trans- 
formed at once. The best result was achieved for the 
I-th quarter, and the poorest for the IV-th quarter. 
For average case of practical applications of the reseau 
camera it would be rather costly to measure all the 
49 crosses on each reseau frame. So the experimental 
bilinear transformation was made for all the 49 crosses, 
using exclusively 9 regularly distributed active crosses, 
but only 4 of them at a time. When transforming 
separately each quarter area of the photograph, we 
got different results, which points out on differences 
of the physical model of errors on different portions 
of the photograph.