**Input**- Direction cosines of normal to plane (sky point facing plane),
*n*1*n*2*n*3 (algorithm 6.12) - Direction cosines of solar azimuth and altitude,
*c*1*c*2*c*3 (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
*-c*1*-c*2*-c*3, the negative of the cosines of solar altitude and azimuth

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