In the radiation method of plane table surveying, the direction of the objects or points to be located are obtained by drawing radial lines along fiducial edge of alidade after getting the objects or points bisected along the line of sight of the alidade. The horizontal distances are then measured and scaled off on the corresponding radial lines to mark their positions on the drawing.

Figure 34.1 Radiation Method of plane table surveying

Let Figure 34.1 be considered in which a plane table is set up at station X and details in the area X plotted by method of radiation.In order to carry out this, first the plane table is set over the station X, clamped and its position is plotted on paper as x. Now, with alidade pivoted at x, salient object points present in the area such as A, B, C, D etc of a building around the plane table got bisected and radial lines are drawn showing their directions. The corresponding field distances XA, XB, XC, XD are measured and scale off on respective radial lines. Thus, plotted their positions as a, b, c, d etc. The plotted positions are then joined to represent the object. In this way, points e, f, g, h are also plotted and joined to get another building corner. The location of a telephone line pillar T plotted as t.

The radiation method of plane table surveying is suitable for locating objects which are within a single tape length (from the location of plane table). The method is convenient if telescopic or digital alidade is used. Otherwise, it is effective when associated with tacheometer or EDM for measurement of horizontal distance.

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