Here are two photographs from a project that IAT completed at the Ocean City City Hall in Ocean City, NJ. These were shot using a Leica R5 which had been modified for use for photogrammetry. A thin glass plate with an array of cross hairs was inserted between the focal point of the lens and the film. This was required for a good camera calibration. (Nowadays with digital SLR camera bodies the cross hairs – or the “reseau” – is no longer required.)
The basis of photogrammetry is “stereoscopy”, or simultaneously viewing the same subject matter from two vantage points. So these two shots capture the same facade from positions to its left and center. They are not shot simultaneously in fact, but sequentially – but in the life of a building they reflect more or less the same instant in time.
Additonal photographs from yet more unique camera locations can be included in a photogrammetric study, so in fact this technique goes well beyond stereoscopy which, technically, is limited to only two views. But for the sake of understanding what is happening in photogrammetry more easily I’ll only talk about two or three views for the moment.