Type II : Measurement along obstacle is possible but not ranging such as bush etc. In this case, either of method of reciprocal ranging or ranging by random line method is being adopted to range a line between stations and subsequently measurement of distance is being carried out. Type III : Both ranging and measurement along the obstacle is not possible such as building. In this case, two perpendicular offsets of equal length are erected from the line before the obstacle and a parallel line is ranged, as shown in Figure 8.6. The parallel line is extended and two perpendicular offsets, of same length as before, beyond the obstacle, are dropped from the line beyond the obstacle. Equivalent distance along a line parallel to ranged line is then measured to get the distance. However, depending on field condition surveyor can apply suitable geometrical /trigonometric concepts to find the unknown distance.
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