The CIPA directive(Comité International de Photogrammetrie Architecturale)
The traditional graphic relief and the photogrammetric relief differ essentially because:
- the first provides a graphic representation in scale, and a series of photographs, which offer a vision mono space, but do not allow to take measurements;
- the second, thanks to a pair of frames, offers a stereo spatial vision and allows to detect the measurements of the objects photographed.
In practice, photogrammetric offers the spatial coordinates (x, y, z) of each point represented on the pair of frames.
When it is not considered sufficient to take the measurements directly from the stereo image, the so-called restitution, that is a graphic representation, is performed, even after years, through which only two are recorded for each point chosen in the photograph coordinates: ITALY - x, y for plan representation;
- x, z for representation in elevation.
It goes without saying that the return only makes sense if "finalized", requiring a choice of points according to a specific purpose, with a time (and, therefore, a cost) proportional to the elements represented.
The proposal, consisting of the establishment of an international archive of photogrammetric surveys of monuments subject to risk of destruction , perhaps appeared utopian half a century ago, both because of the difficult use of glass plates in photogrammetry duplication and transport, both for the existence of optical-mechanical restitutors, which accepted only frames of cameras with well-defined format and focal length.
Today all the genius of the idea emerges, since, with the use of digital photography, all the problems of archiving and restitution have disappeared.