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of the coordinate parallax measurements and left these radial displacements uncorrected - see 
Figure 6 - to become the measure of relative radial error at the fixed points used in the adjustment 
procedure. Contours of relative radial displacement can be interpolated between the points of 
adjustment - see Figure 7 - to determine corrections of radial error for all other displacement 
data [4]. Correction of relative radial error was sufficient, with no absolute determinations 
required of the flatness of any one photographic plate in the camera or in the laboratory. 
With analytical correction of radial error the standard error of measurement was reduced 
to almost one-tenth of its magnitude for the camera in stereophotogrammetric use, 
  
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o 4 2 3 4 5 CM o 10 20 30 40 so 4m 
SCALE OF PLATES SCALE OF RESIDUALS 
Figure 6. Residual discrepancies between two photogrammetric plates from the same camera after adjustment at 
fiducial marks 1-4, outlines of camera pressure plates 5-8, and fixed control points in object space recorded in the 
photographic image 10-18, on the basis of tangential components only of measured parallaxes between the two plates. 
Residuals are also shown at six other fixed points not used in the adjustment procedure. 
The ruined photogrammetric plate of Figure 8, exposed and then lightstruck during the 
insertion of the cover of the plateholder, reveals striking irregularities of surface of the emulsion. 
The emulsions of other photogrammetric plates have areas which are rough to the touch when 
being loaded in darkness. Radial error must be more random and irregular than plate bending 
alone would suggest. 
Instead of interpolating relative radial error between points as shown in Figure 6 - or 
between the points of a reseau - a more nearly automatic method for correction of radial error 
in the measurement of structural movements has been proposed before [5] which can compensate 
better for random and limited irregularities of the emulsion surface. If at each camera station a 
second photograph is taken immediately after rotation of the camera axis to a divergent orientation 
angle, there will be an overlapping portion of the two images within which the tangential displace- 
ments of any single point around two fiducial centers can be resolved by intersection into coordinate 
displacements in px and py in which the uncertainty of determination of radial error approaches ) - 
the magnitude of tangential error, instead of being as much as twenty times greater. (This 7 NN 
procedure can be adapted to analytical photogrammetry of static subjects - see Figure 10). : 
—8—