/usr/share/radiance/tregsrc.cal is in radiance-materials 4R1+20120125-1.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 | { RCSid $Id: tregsrc.cal,v 1.2 2009/07/01 00:39:34 greg Exp $ }
{
Tregenza patch positions & solid angles
Greg Ward June 2005
The Tregenza sky uses 145 patches, with patch 1 pointing due
North at the horizon, and continuing around to the East to
patch 30, which comprises the first altitude row (alt = 6 degrees).
Each successive row increases altitude by 12 degrees, with the
final altitude at the zenith (90 degrees). Azimuth is evenly
divided among 30, 30, 24, 24, 18, 12, 6, and 1 divisions per row.
Input is Tbin from 1-145 and optional random variables x1 & x2
Output is Dx Dy Dz theta (degree full angle of source)
}
DEGREE : PI/180;
x1 = .5; x2 = .5; { default random variable settings for midpoint }
Trow = if(30.5-Tbin, 1,
if(60.5-Tbin, 2,
if(84.5-Tbin, 3,
if(108.5-Tbin, 4,
if(126.5-Tbin, 5,
if(138.5-Tbin, 6,
if(144.5-Tbin, 7, 8) ) ) ) ) ) );
cols_row = select(Trow, 30, 30, 24, 24, 18, 12, 6, 1);
Tcol = Tbin - select(Trow, 0, 30, 60, 84, 108, 126, 138, 144);
Tazi_width = 2*PI / cols_row;
TAH : 12*DEGREE;
Tazi = (Tcol - .5 - x2)*Tazi_width;
Talt = (Trow - x1)*TAH;
Tomega = if(144.5-Tbin,
Tazi_width*(sin(TAH*Trow) - sin(TAH*(Trow-1))),
0.0344199465 );
cos_talt = cos(Talt);
Dx = sin(Tazi)*cos_talt;
Dy = cos(Tazi)*cos_talt;
Dz = sin(Talt);
theta = 2/DEGREE * acos(1 - Tomega/(2*PI));
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