{ RCSid: $Id: illum.cal,v 2.8 2003/02/22 02:07:23 greg Exp $ }
{
	Coordinate computations for mkillum output.

	There are no arguments for the spherical case:

	il_alt		- Altitude (1 to -1) for spherical coordinates
	il_azi		- Azimuth (0 to 2*PI) for sphere

	For the hemispherical case, A1-A9 are the unit vectors for the
	hemisphere's coordinate system:

	il_alth		- Altitude (1 to 0) for hemispherical coordinates
	il_azih		- Azimuth (0 to 2*PI) for hemisphere
}

norm_rad(r) : if( r, r, r+2*PI );

il_alt = Dz;
il_azi = norm_rad(Atan2(Dy, Dx));

il_alth = sq(-Dx*A7-Dy*A8-Dz*A9);
il_azih = norm_rad(Atan2(-Dx*A4-Dy*A5-Dz*A6, -Dx*A1-Dy*A2-Dz*A3));
