Full text: Commissions V, VI and VII (Part 5)

  
In other cases the advantage of stereophotogrammetric plotting at the first order 
instrument is in seeing the distortions of architectural and photogrammetric geometry directly 
revealed during instrument movements in the coordinate system established for the optical model. 
Often - even after prolonged orientàtion of the instrument - these distortions are not insignificant. 
They may disappear within the standard error acceptable in the drawing of large historical 
structures at relatively small scale, but they have been seen, and error has become a geometrical 
reality rather than a mathematical abstraction. It is a condition to attack, for there are situations 
which demand distinguishing between the deformations of architectural and photogrammetric 
geometry. 
The bowing outwards of the top of a wall in an architectural optical model - with minor 
influence on the vertical dimensioning of a facade - may indicate uncorrected divergence of two 
camera axes in the exterior orientation, the bowing of a photogrammetric plate, or the actual 
progressive inclination outwards of a wall pushed by expanding and contracting roof trusses which 
can ultimately drop within the displaced wall structure. An actual deformation of architectural 
geometry may have serious meaning; it is always of interest to the architect, who must find 
photogrammetry inadequate if it leaves him in doubt of the actuality of architectural deformations 
he has seen. 
  
Figure 1. Camera Test Field, 1960, Professor Hallert's Institute, Royal Institute of Technology, Stockholm, Sweden. 
The deformations of the test wall in stereoscopic view are due to lack of film flatness in wide angle photography. 
  
Figure 2. Gothic Cathedral at Linkóping, Sweden, 1964. The actual outward lean of the piers and wall may be caused 
oy the thrusts of the vaults and the original yielding of tension members of the roof truss before the addition of exterior 
uttresses. 
  
 
	        
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