Data Processing Methods in Correcting
Stereoautographs
By S. Thorén, Photogrammetric division, Kjessler & Mannerstrále AB,
Consulting Engineers and Architects, Stockholm 19, Sweden
Precision instruments are generally provided with adjustment points
which require attention from time to time, in order to ensure that they
function accurately. If errors of importance which cannot be corrected
in the instrument itself are found, they have to be treated with proper
methods outside the instrument, Corrections added by mathematical
methods to results produced in an uncorrected instrument may in
certain circumstanses increase the accuracy or economy.
The adjustment of 1 st and 2 nd order instruments is a difficult
matter, and thus the manufacturers always deliver the apparatus to the
customer ready for use, the erecting engineer completing his installa-
tion with the necessary adjustments and final tests.
However, these instruments decrease in accuracy, sometimes rapidly,
during the running in period due to release of stresses and ageing of
castings. Heavily loaded details will after a long time show minor de-
formations and later wear will be noticed.
Correcting these defects requires particular knowledge of the instru-
ment and good experience in fine mechanical work, which is not often
found in stereoperators. With this in mind the manufacturers give a
very simplified version of the adjustment procedure in the instrument
manual. Often a main correction is made with an optical element nearest
the picture, and this simplification naturally limits the final accuracy.
In fact there are many elements which are interdependent. For this
reason it is very difficult to relate grid measurements to the individual
correction, and it can be readily understood that the "step by step"
method is very laborious. A wrongly made correction at a certain stage
will perhaps seriously affect the next stages.
Usually it is recommended to adjust at an altitude of 60 % of the
maximum model altitude.
maximum model altitude. For each camera, coordinates of the grid
intersections are measured and from their deviations from theoretical
values the standard errors m, and m, are found. At the end of the
whole procedure a long base is introduced, and elevations of the grid
9
=
