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{ RCSid $Id: cieskyscan.cal,v 2.1 2024/02/08 02:26:01 greg Exp $ }
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{
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Compute CIE standard sky scanner bin (cbin)
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Different azimuth origin, alignment, and winding than Tregenza/Reinhart
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RHS - right-handed system?
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JTR - bin jitter/mixing amount
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Dx,Dy,Dz - Incident direction (normalized, towards surface face)
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rNx,rNy,rNz - Surface normal (normalized, away from surface)
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Ux,Uy,Uz - Up direction vector (does not need to be normalized)
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Modified from reinhartb.cal
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Feburary 2024 G. Ward
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}
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{ Useful factors and functions }
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DEGREE` : PI/180;
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mod`(n,d) : n - floor(n/d)*d;
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Asin(x) : if(x-1, PI/2, if(-1-x, -PI/2, asin(x))) / DEGREE;
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Atan2(y,x) : mod( atan2(y,x)/DEGREE, 360);
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{ Set to -1 for left-handed coordinate system }
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RHS = 1;
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{ Sharp bin boundaries by default }
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JTR = 0;
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{ Default axis orientation (+Y == north) }
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rNx = 0; rNy = 0; rNz = -1;
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Ux = 0; Uy = 1; Uz = 0;
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{ Compute oriented axis angles }
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inc_dz = -Dx*rNx-Dy*rNy-Dz*rNz;
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inc_rx = -RHS*(Dx*(Uy*rNz-Uz*rNy) + Dy*(Uz*rNx-Ux*rNz) + Dz*(Ux*rNy-Uy*rNx));
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inc_ry = Dx*Ux+Dy*Uy+Dz*Uz + inc_dz*(rNx*Ux+rNy*Uy+rNz*Uz);
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r_alt = Asin(inc_dz);
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c_azi = Atan2(-inc_rx,-inc_ry);
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calpha : 90/7.5; { Separation between rows in degrees }
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{ Number of patches per row }
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cnaz(r) : select(r+1, 30, 30, 24, 24, 18, 12, 6, 1);
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CNR : cnaz(-1);
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caccum(r) : if(r-.5, cnaz(r-1) + caccum(r-1), 0);
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{ Random perturbation for final bin # }
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jtr1 = JTR*(.5 - rand(1.958*Dx - 5.386*Dy - 3.772*Dz));
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jtr2 = JTR*(.5 - rand(-6.334*Dx - 2.165*Dy + 7.953*Dz));
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c_row = if(JTR, min(max(0,floor(r_alt/calpha + jtr1)),CNR-1),
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floor(r_alt/calpha));
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c_inc = 360/cnaz(c_row);
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c_aznf = floor( mod(c_azi+if(JTR,jtr2*c_inc,0), 360) / c_inc );
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fwd_row = floor(c_row/2+1.25) - c_row/2 - .75;
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c_azn = if(fwd_row, c_aznf, cnaz(c_row)-1 - c_aznf);
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{ Final bin value, -1 for "ground" }
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cbin = if (r_alt, caccum(c_row) + c_azn, -1);
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Ncbins : caccum(CNR); { total number of bins }
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