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{ RCSid $Id: klems_quarter.cal,v 1.6 2022/07/14 02:52:02 greg Exp $ }
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{
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Compute interior bin for quarter Klems BSDF basis (0-40)
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Returns -1 for wrong-side rays
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Modified from klems_full.cal
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7/18/2014 G. Ward
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}
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DEGREE` : PI/180;
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mod`(n,d) : n - floor(n/d)*d;
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Acos(x) : if(x-1, 0, if(-1-x, PI, acos(x))) / DEGREE;
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kqpola(r) : select(r, 9, 27, 45, 63, 90);
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KQAPS : kqpola(3) - kqpola(2);
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kqnaz(r) : select(r, 1, 8, 12, 12, 8);
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kqaccum(r) : if(r-.5, kqnaz(r) + kqaccum(r-1), 0);
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kqfindrow(r, pol) : if(r-kqpola(0)+.5, r,
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if(pol-kqpola(r), kqfindrow(r+1, pol), r) );
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RHS = 1; { Set to -1 for left-handed system }
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JTR = 0; { Sharp bin boundaries by default }
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{ Uniform perturbation function }
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kjtr(n) = if(JTR, JTR*(.5 - rand(n*(9.54*Dx - 5.11*Dy + 1.37*Dz - 6.71))), 0);
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kazn(azi,inc) = floor( mod(azi + inc*(.5+kjtr(2)), 360) / inc );
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kqbin2(pol,azi) =
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select(kqfindrow(1, pol),
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kazn(azi,360/kqnaz(1)),
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kqaccum(1) + kazn(azi,360/kqnaz(2)),
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kqaccum(2) + kazn(azi,360/kqnaz(3)),
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kqaccum(3) + kazn(azi,360/kqnaz(4)),
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kqaccum(4) + kazn(azi,360/kqnaz(5))
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);
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kqbin1(zv,yv,xv) = if(zv, kqbin2(min(max(0, Acos(zv) + KQAPS*kjtr(1)), 90),
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atan2(yv,xv)/DEGREE),
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-1);
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kqbin(Nx,Ny,Nz,Ux,Uy,Uz) = kqbin1(-Dx*Nx-Dy*Ny-Dz*Nz,
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-Dx*Ux-Dy*Uy-Dz*Uz + (Nx*Dx+Ny*Dy+Nz*Dz)*(Nx*Ux+Ny*Uy+Nz*Uz),
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-RHS*(Dx*(Uy*Nz-Uz*Ny) + Dy*(Uz*Nx-Ux*Nz) + Dz*(Ux*Ny-Uy*Nx)));
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Nkqbins : kqaccum(kqnaz(0)); { Number of bins for one elevation }
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