Shadow length--Algorithm 1.16

This algorithm gives the length L of shadow cast by a point H metres high above an inclined surface.

Input
Direction cosines of normal to plane (sky point facing plane), n1 n2 n3 (algorithm 6.12)
Direction cosines of solar azimuth and altitude, c1 c2 c3 (algorithm 1.24)
Perpendicular height of point above plane, H

Equation

Source
General theory of analytic geometry

Note
Algorithm 5.15 can be used to calculate the coordinates of the shadow point. This is done by taking a line from the tip of the obstruction, in the direction of the solar beam, to its intersection with the plane. The direction cosines of the solar beam are -c1 -c2 -c3, the negative of the cosines of solar altitude and azimuth


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