Photogrammetry

Topics to be covered in this post are:
1) Terrestrial and Aerial photographs,
2)Aerial Camera and height displacements in vertical photographs,
3)Stereoscopic vision and stereoscopies,
4)Height determination from parallax measurement,
5)flight planning,
6)Plotting by radial line method,
7)Principle of photo interpretation and photogrammetric monitoring in Civil Engineering.
8)Introduction to remote sensing and its systems,
9)Concept of G.I.S. and GPS - basic components,
10)data input, storage and output.
Photogrammetry and types of photographs:
Photogrammetry is an art or science of preparation of maps, plans, or 3D models of areas, using the photographs taken by the photogrammetric cameras. It is broadly classified into two categories,
(1) Terrestrial Photogrammetry  (2) Aerial Photogrammetry
In Terrestrial photogrammetry the photos are taken on the surface of the earth, and these photos are used to interpret the 3D models, or the dimensions of the objects. Terrestrial photogrammetry is not suitable for the preparation of the contour maps, or the topographical maps. The photos taken on the surface of the earth are known as the terrestrial photographs.
Aerial photogrammetry is another branch in which we take the photographs from the air. Cameras are fixed in the air-crafts, which take the flight over the area to be surveyed and the suitable cameras take the photographs from the altitude of the air craft. The photos taken from the air are known as the Aerial photographs.
The photographs can be taken , as vertical photographs, tilted photographs, or the angular photographs. In vertical photographs, the camera axis coincides with the plumb line. In the tilted photographs the camera axis is un-intentionally tilted to the plumb line at an angle of less than 3 degrees.
In the Angular photographs the camera axis makes a certain angle with the plumb line, which is kept so intentionally.

Relief Displacement: Relief displacement is the result of the perspective projection of the true ground points in the  image captured in the photograph. Two points on the ground one above the other, will look at some horizontal distance in the perspective projection, or the photograph. This horizontal distance between the two such point ( generally the point under consideration are, ground point, and the datum) under consideration is known as the relief displacement.
In the above figure, dc is the relief displacement. d is the projection of the A' while c is the projection of the A on the vertical image taken from the aircraft. Actually they should overlap each other, if they were photographed along the camera axis. 

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