Figure 4, Diagram showing standard positions of survey control at the level of the camera horizon and the series of 
planes investigated for systematic error caused by uncorrected elements of orientation. 
This limit of accuracy is considered to be the result of radial error caused by lack of e e 
flatness of photogrammetric plates and emulsions. In the deep optical model, radial error becomes 
an irregular and unpredictable disturbance of the inner orientation of the wide-angle cameras, of 
relatively short focal length, which are generally in use in architectural photogrammetry. Analytical 
methods are required to isolate and remove this radial error. 
Isolation of Radial Error in Measurement of Movements in Architectural and Engineering Structure 
  
Photogrammetric projects in the measurement of movements in architectural and 
engineering structure have revealed the extent of radial error in plates exposed in a phototheodolite 
especially developed for architectural surveys. The focal length of this camera is 151.66 mm. 
with a format of 13 x 18 cm. When first tested in Professor Bertil Hallert' s institute in Stockholm 
in 1960 it was found necessary to replace all the springs in the plateholders, because, not 
coinciding well with the pressure plates of the camera frame, they introduced a systematic radial 
error of bowing every plate almost 160um. out of flatness [2]. These corrections were made 
before the camera was used in the measurement of structural movements. 
In photogrammetric measurement of movement in architectural and engineering structure 
the basic data are relative measurements - parallaxes - between pairs of plates photographed at 
different times with the same camera at the same camera station along the same camera axis. 
The correspondence between successive pairs of plates which are measured together should 
effectively eliminate systematic. error caused by lens defects and make possible the measurement 
of movements of structure with greater accuracy than measurement of the structure itself. 
The plates were measured together in a Wild StK Stereocomparator with the intention 
that adjustment of the two plates on the recorded fiducial marks and pressure plates of the camera 
frame and on fixed points in object space recorded in the photogrammetric image would determine 
minor displacements in returning to the camera station and minor rotations of the camera axes. 
The adjusted data would reveal small structural movements by significant parallaxes remaining k 
at points on the structure photographed. At first, the significance of all measurements of the e © 
plates seemed in doubt when discrepancies of as much as 100 Hm. appeared in the measurement 
between left and right fiducial marks in pairs of "ultra flat" photogrammetric plates. It became 
essential to isolate the large radial error this indicated. 
=6-