The application of photogrammetry to architecture has been an infrequent 
exercise for photogrammetrists whose natural tendency should be to reproduce the 
conditions and procedures of aerial photogrammetry in the plotting and drawing of 
buildings. Sometimes this is possible, and an entire facade may be photographed in 
stereopair with camera axes normal to the facade, with relative orientation following 
the procedure for nearly vertical aerial photographs of essentially flat terrain, and 
with control measurements on the plane of the facade to determine absolute orientation 
and scale. More often than not, however, the building and its location do not permit 
this particular photogrammetric procedure. First the camera must be inclined up- 
wards. Then in indeterminate seas of grass or blank sky the points are lost at which, 
in aerial stereopairs, the elements of relative orientation can be isolated. Finally the 
orientation which satisfied the general plane of the facade reveals its weakness when 
plotting is pushed in depth to distant towers or to nearby steps and terraces. 
It is the need for accuracy in great depth of plotting that places architectural 
photogrammetry firmly in the category of terrestrial photogrammetry. The studies 
of such men as Professor Bertil Hallert of Sweden of the problems of terrestrial 
photogrammetry have considerable application in the photogrammetry of architecture. 
Professor Hallert's "Determination of the Accuracy of Terrestrial Stereophotogram- 
metric Procedures, "' published in the March,1955 issue of Photogrammetric Engi- 
neering, describes the effect of small errors of the convergence of camera axes upon 
the plotting of a plane and upon the propagation of error in depth of plotting. I have