104 PHOTO INTERPRETATION PICTURE, COLWELL 
tower has six legs. On the left photo, the hexagonal shape of each of the two horizontal 
systems of wliite cross-braces is clearly seen. But even at this point, the photo inter- 
preter probably still fails to comprehend fully the geometry of the right photo. For he 
can scarcely believe that the upper of the two quadrilaterals seen on the right photo is 
composed of two cross-braces from the lower hexagon plus two cross-braces from the 
upper hexagon. When he is told that, at the time the right photo was taken the x, y and 
  
Fig. 10. Two overlapping photos of the same feature shown in Fig. 9. Note 
how different the structural details of the water tower appear to be on the 
left photo as compared with the right. (Although these photos are mounted 
as a stereogram, there is too much parallax to permit easy stereoscopic 
study of the water tower.) 
z coordinates of the camera station were precisely correct for creating the illusion that 
the water tower has only four legs, the deflated photo interpreter is likely to exclaim, 
“what a coincidence!” But is it such a great coincidence, after all? A moment’s reflection 
shows that there are at least six other camera stations from which exactly the same 
result might have been achieved; or alternatively, that even with the same azimuth 
orientation, this water tower would have appeared much the same on this photo if 
situated at any of six other spots within the area photographed. It therefore, is my belief 
that the frequency of this type of misinterpretation of photos is far greater than we or- 
dinarily realize, and that the remedy is to be found only through a clearer understanding 
of the geometry of the photographs. In brief, pictures don’t lie, for they record objects 
in unbiased conformity to well-known mathematical and physical laws; but they cer- 
tainly can be misinterpreted by one lacking full appreciation of how these laws affect 
the appearance of photographic images. This point is of such importance and the dif- 
ficulty can exist in so many forms that additional examples should be given. 
Figure 11A is another example of the misinterpretation that can be made of an 
aerial photo when its geometry is not fully appreciated. Most any photo interpreter might 
identify the shorter vehicle as a “compact” or “economy” car, and the longer one as a 
streamlined limousine. Actually both are of about the same length. The photo interpreter 
may be readily convinced of this fact when he is shown more of the photo from which 
Figure 11A was taken (see Fig. 11B). It would be a strange coincidence, indeed, if all 
the cars and even the trucks going in one direction on the freeway were short and stubby, 
while all of those going in the opposite dirrection were very elongate. When the photo 
interpreter is told that this photograph was taken with a camera having image motion 
compensation, he is likely to make the superficial comment that this obviously explains 
why the images of moving objects appear as they do in this figure. His deficiencies in