The Combined Effects of Tilt and Relief Displacement (Especially for GATE-Geospatial 2022)

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It has already been shown that tilting of the aerial photograph causes image displacement radial from the isocenter on a flat plane. With the presence of relief, the image is further displaced as a result of relief displacement caused by the central projection of the aerial photograph, which is radial from the nadir point. Thus, an aerial photograph is really the result of the interaction of these two processes. Moffitt has idealised their combined effects graphically in below Figure where the displacement of five points at various portions of the aerial photograph is examined.

Combined Effects of Tilt and Relief Displacements

In this diagram, the various positions of the point before and after tilting and/or relief displacement are indicated; thus number 1 indicates the correct position of the point at datum, number 2 indicates the position of the point after relief displacement, and number 3 indicates the position of the point after tilt displacement. It is noteworthy that for points A and B the tilt and relief displacements tend to act in opposite directions; for points C and D, the two displacements occur in the same direction; and for point E there is no tilt displacement (only relief displacement) because it lies on the axis of tilt. From this diagram, one can see the complexity of tilts and relief displacements in affecting the geometry of the aerial photograph.

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