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/* Copyright (c) 1996 Regents of the University of California */ |
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/* Copyright (c) 1997 Regents of the University of California */ |
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#ifndef lint |
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static char SCCSid[] = "$SunId$ LBL"; |
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double |
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hacuity(La) /* return visual acuity in cycles/degree */ |
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double La; |
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{ /* data due to S. Shaler (we should fit it!) */ |
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#define NPOINTS 20 |
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static float l10lum[NPOINTS] = { |
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-3.10503,-2.66403,-2.37703,-2.09303,-1.64403,-1.35803, |
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-1.07403,-0.67203,-0.38503,-0.10103,0.29397,0.58097,0.86497, |
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1.25697,1.54397,1.82797,2.27597,2.56297,2.84697,3.24897 |
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}; |
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static float resfreq[NPOINTS] = { |
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2.09,3.28,3.79,4.39,6.11,8.83,10.94,18.66,23.88,31.05,37.42, |
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37.68,41.60,43.16,45.30,47.00,48.43,48.32,51.06,51.09 |
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}; |
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double l10La; |
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register int i; |
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/* check limits */ |
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if (La <= 7.85e-4) |
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return(resfreq[0]); |
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if (La >= 1.78e3) |
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return(resfreq[NPOINTS-1]); |
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/* interpolate data */ |
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l10La = log10(La); |
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for (i = 0; i < NPOINTS-2 && l10lum[i+1] <= l10La; i++) |
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; |
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return( ( (l10lum[i+1] - l10La)*resfreq[i] + |
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(l10La - l10lum[i])*resfreq[i+1] ) / |
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(l10lum[i+1] - l10lum[i]) ); |
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#undef NPOINTS |
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{ |
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/* functional fit */ |
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return(17.25*atan(1.4*log10(La) + 0.35) + 25.72); |
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} |
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