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greg |
1.1 |
{ RCSid $Id$ } |
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{ |
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Compute bin numbers corresponding to Tregenza sky discretization |
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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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In addition to the bin numbers 1-145 corresponding to this |
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standard, bin 0 is used for the ground plane (altitude < 0). |
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Input is normalized ray direction (Dx,Dy,Dz). The Y-axis is |
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assumed to point North, and the X-axis East, matching the |
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convention set by gensky(1). |
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Greg Ward May 2005 |
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} |
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DEGREE : PI/180; |
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Asin(x) : if(x-1, PI/2, if(-1-x, -PI/2, asin(x))); |
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posangle(a) : if(-a, a + 2*PI, a); |
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Atan2(y,x) : posangle(atan2(y,x)); |
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alt = Asin(Dz)/DEGREE; |
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azi = Atan2(Dx,Dy)/DEGREE; |
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tazi(inc) = if(azi-(360-.5*inc), 0, floor((azi+.5*inc)/inc)); |
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tbin = if(-alt, 0, |
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select(floor(alt/12) + 1, |
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1 + tazi(12), |
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31 + tazi(12), |
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61 + tazi(15), |
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85 + tazi(15), |
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109 + tazi(20), |
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127 + tazi(30), |
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139 + tazi(60), |
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145 |
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) ); |
