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{ RCSid $Id$ }
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{
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Tregenza patch positions & solid angles
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Greg Ward June 2005
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The Tregenza sky uses 145 patches, with patch 1 pointing due
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North at the horizon, and continuing around to the East to
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patch 30, which comprises the first altitude row (alt = 6 degrees).
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Each successive row increases altitude by 12 degrees, with the
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final altitude at the zenith (90 degrees). Azimuth is evenly
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divided among 30, 30, 24, 24, 18, 12, 6, and 1 divisions per row.
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Input is Tbin from 1-145
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Output is Dx Dy Dz theta (degree full angle of source)
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}
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DEGREE : PI/180;
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Trow = if(30.5-Tbin, 1,
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if(60.5-Tbin, 2,
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if(84.5-Tbin, 3,
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if(108.5-Tbin, 4,
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if(126.5-Tbin, 5,
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if(138.5-Tbin, 6,
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if(144.5-Tbin, 7, 8) ) ) ) ) ) );
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cols_row = select(Trow, 30, 30, 24, 24, 18, 12, 6, 1);
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Tcol = Tbin - select(Trow, 0, 30, 60, 84, 108, 126, 138, 144);
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Tazi_width = 2*PI / cols_row;
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TAH : 12*DEGREE;
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Tazi = (Tcol - 1)*Tazi_width;
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Talt = (Trow - .5)*TAH;
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Tomega = if(144.5-Tbin,
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Tazi_width*(sin(TAH*Trow) - sin(TAH*(Trow-1))),
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0.0344199465 );
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cos_talt = cos(Talt);
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Dx = sin(Tazi)*cos_talt;
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Dy = cos(Tazi)*cos_talt;
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Dz = sin(Talt);
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theta = 2/DEGREE * acos(1 - Tomega/(2*PI));
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