Let us consider two-dimensional objects, meaning by those those whose third dimension is negligible with respect to the observation distance. This is the case, for example, of the prospect of the cathedral of Bari, of which we see the photograph on the left. This photograph was taken with the Wild P31 super wide-angle metric camera, thanks to which the vertical position of the sensitive surface can be given for certain. Taking for granted the verticality of the facade of the cathedral, we can believe that, thanks to the parallelism between the two surfaces, the photographic image of the prospect is a scaled representation of the same (hence the use of the program to detect distances).

By intersecting the beam of rays projecting the image with a vertical plane, it is not difficult to detect the similarity between the two triangles having the center of projection as a common vertex and the object and the image respectively as base. Consequently there is the proportion a / A = d / D, that is, if d = D / 100 the image will be in 1/100 scale. The figure on the left shows the scheme for the design of a room with a pinhole for taking a photoplan in the desired scale.