/usr/share/radiance/tregenza.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 | { RCSid $Id: tregenza.cal,v 1.4 2009/09/15 00:17:36 greg Exp $ }
{
Compute bin numbers corresponding to Tregenza sky discretization
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.
In addition to the bin numbers 1-145 corresponding to this
standard, bin 0 is used for the ground plane (altitude < 0).
Input is normalized ray direction (Dx,Dy,Dz). The Y-axis is
assumed to point North, and the X-axis East, matching the
convention set by gensky(1).
Greg Ward May 2005
}
DEGREE : PI/180;
Asin(x) : if(x-1, PI/2, if(-1-x, -PI/2, asin(x)));
posangle(a) : if(-a, a + 2*PI, a);
Atan2(y,x) : posangle(atan2(y,x));
alt = Asin(Dz)/DEGREE;
azi = Atan2(Dx,Dy)/DEGREE;
tazi(inc) = if(359.9999-.5*inc - azi, floor((azi+.5*inc)/inc), 0);
tbin = if(-alt, 0,
select(floor(alt/12) + 1,
1 + tazi(12),
31 + tazi(12),
61 + tazi(15),
85 + tazi(15),
109 + tazi(20),
127 + tazi(30),
139 + tazi(60),
145
) );
Ntbins : 146; { total number of bins }
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