Photogrammetric Surveying

 Photogrammetric Surveying:

Photogrammetric surveying or photogrammetry is the branch of surveying in which maps are prepared from the photographs taken from the ground or air stations. With the advancement of photogrammetric techniques, photographs are also being used for the interpretation of geology, and classifications of soils and crops.

Principle of Photogrammetry and its limitations:
The principle of the photogrammetric survey in its simplest form is very similar to that of the plane survey. The only difference is that most of the work which in the plane table survey is executed in the
field, is done in the office. The principle point of each photograph is used as a fixed station in plane table surveys and rays are drawn to get points of intersections very similar to those used in plane table.

Photogrammetry is particularly suitable for topographical or engineering surveys and also for those projects demanding higher accuracy.The photogrammetry is rather unsuitable for dense forest and flat sands due to  difficulty of identifying points upon the pair of photographs.It is also unsuitable for flat terrain where contour plans are required because interpretation of contours becomes difficult in the absence of spirit levelled heights.
From the above points it is clear that photogrammetry may be most suitable for mountaineous and hilly terrain with less vegitations.