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Figure 3. Courtyard of S. Carlo, Rome, Italy, 1960. The bulging of the side columns in stereoscopic view are due to 
lack of film flatness in wide angle photography, 
Three film stereopairs are shown in exaggerated illustration of architectural and 
photographic deformations in photogrammetry. Figure 1 and Figure 3 were taken with a wide 
angle camera subsequently adjusted by the manufacturer to reduce distortions and buckling of the 
film plane caused by the paper backing. The test field in Figure 1 contained no actual deformation 
such as is shown here; and the columns of Figure 3 are deformed in a manner which could not 
occur naturally. Figure 2 shows genuine deformation in architecture, which could be observed 
on the exterior of the building also, where walls inclining outwards were braced by buttresses 
with vertical outer faces. 
Survey Control and Exterior Orientation 
  
When distortions are observable in the optical model, their source is first sought in the 
exterior orientation of the photogrammetric stereopair. This orientation has been adjusted at the 
points of survey control and then along what should be regular planes and edges within the archi- 
tectural model. 
Figure 4 is a diagram of standard positions of survey control established with poles 
driven into the ground before an architectural subject and targetted at the level of the camera 
horizon. In situations which do not permit the use of survey poles, the control is targetted at the 
level of the camera horizon on existing walls, light standards, fences, etc.. in as nearly similar 
a pattern as possible. This pattern of control allows a rapid adjustment in the A7 Autograph of 
the absolute orientation of ,, «, , by, , w, and «,.[1] Measured distances between the 
points of survey control on the site and in the model and y parallax measurements within the 
optical model are the bases for orientation of o, , ¢, and bz,. 
Figure 4 also shows a series of horizontal and vertical planes in positions typical of 
architectural surfaces and edges above, below, parallel and normal to the base between camera 
positions, while Figure 5 shows the systematic distortion of these planes due to one uncorrected 
element of exterior orientation w, . 
Diagrams such as Figure 5 are useful to the operator of the A7 Autograph as he scans the 
optical model in the orientation process. However, there are residual discrepancies between the 
orientations of ¢,, ¢, , and bz, determined from survey control measurements in the plane of 
the camera horizon and orientations of the same elements which minimize distortions in architec- 
tural planes in the optical model. When the camera axis is inclined upwards - as is often 
necessary in recording tall buildings at close quarters - these discrepancies appear in the 
orientations of K,, K,, w, , and «o, also. If the plotting is in planes of greatly varying depth in 
the optical model, it is often desirable to have measurements upon these planes in object space 
to be able to change scale in the model to maintain an overall average error of less than 1 part in 
1200 in plotting major dimensions in architecture.