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greg |
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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)); |
