ADJUSTMENT OF ilL) CENTZRING OF IMAGES IN PAOJSCTORS WITH 
THE AID OF FIDUCIAL MARKS 
  
Le Ottoson 
Stockholm 70 
Photographic pictures are generally centered in the 
projectors of a photogrammetric instrument by the aid of 
four fiducial marks in the image (camera) and in the pro- 
jector. This operation implies & measurinz procedure with 
superfluous observations, and can seldom be performed with 
perfect accuracy. Even if the two sets of fiducial marks 
in the camera and the instrument are exactly congruent, 
discrepancies must always be expected in the centering 
procedure due to observational errors, film shrinkage etc. 
Three different centering errors may occur, namely 
two translations and one rotation of the picture. The in- 
fluence of regular film shrinkage may be compensated at 
the plotting by changing the principle distance. The co- 
ordinate errors in the projection plane, which are caused 
by centering errors and regular film shrinkage, can, for 
the normal case, be written as is shown in the wellknown 
expressions (1) and (2). See fig. 1. 
3 m Xdc 
dx = C dx, yda - Ta (1) 
dy = - Ë dy + xda - LC (2) 
yt c Yo e c 
The centering errors dy, and da will cause y-parallexes 
in a photogrammetric model. The subscripts 1 and 2 refer 
to the errors of the left and right projector respectively. 
Thus we have