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include <mach.h>
include "../lib/fitsky.h"
# AP_CROSSCOR -- Procedure to compute the sky value by calculating the
# cross-correlation function of the histogram of the sky pixels and
# a Gaussian function with the same sigma as the sky distribution.
# The peak of the cross-correlation function is found by parabolic
# interpolation.
int procedure ap_crosscor (skypix, coords, wgt, index, nskypix, snx, sny, k1,
hwidth, binsize, smooth, losigma, hisigma, rgrow, maxiter, sky_mode,
sky_sigma, sky_skew, nsky, nsky_reject)
real skypix[ARB] # array of sky pixels
int coords[ARB] # array of sky coordinates for region growing
real wgt[ARB] # array of weights for rejection
int index[ARB] # array of sort indices
int nskypix # the number of sky pixels
int snx, sny # the maximum dimensions of sky raster
real k1 # half-width of the histogram in sky sigma
real hwidth # the input sky sigma
real binsize # the size of the histogram in sky sigma
int smooth # smooth the histogram before fitting (not used)
real losigma, hisigma # upper and lower rejection limits
real rgrow # region growing radius in pixels
int maxiter # maximum number of rejection cycles
real sky_mode # computed sky value
real sky_sigma # computed standard deviation of the sky pixels
real sky_skew # computed skew of sky pixels
int nsky # number of sky pixels used in fit
int nsky_reject # number of sky pixels rejected
double dsky, sumpx, sumsqpx, sumcbpx
int nreject, nbins, nker, nsmooth, ier, i, j
pointer sp, x, hgm, shgm, kernel
real dmin, dmax, hmin, hmax, dh, kmin, kmax, locut, hicut, sky_mean, cut
real sky_zero
int ap_grow_hist2(), aphigmr()
real ap_asumr(), apmedr()
begin
# Initialize.
nsky = nskypix
nsky_reject = 0
sky_mode = INDEFR
sky_sigma = INDEFR
sky_skew = INDEFR
if (nskypix <= 0)
return (AP_NOSKYAREA)
# Set up initial guess at sky mean, sigma and skew.
sky_zero = ap_asumr (skypix, index, nskypix) / nskypix
call ap_ialimr (skypix, index, nskypix, dmin, dmax)
call apfimoments (skypix, index, nskypix, sky_zero,
sumpx, sumsqpx, sumcbpx, sky_mean, sky_sigma, sky_skew)
sky_mean = apmedr (skypix, index, nskypix)
sky_mean = max (dmin, min (sky_mean, dmax))
# Compute the width and bin size of the histogram.
if (! IS_INDEFR(hwidth) && hwidth > 0.0) {
hmin = sky_mean - k1 * hwidth
hmax = sky_mean + k1 * hwidth
dh = binsize * hwidth
} else {
cut = min (sky_mean - dmin, dmax - sky_mean, k1 * sky_sigma)
hmin = sky_mean - cut
hmax = sky_mean + cut
dh = binsize * cut / k1
}
# Compute the number of bins in and the width of the kernel.
if (dh <= 0.0) {
nbins = 1
nker = 1
nsmooth = 1
dh = 0.0
} else {
nbins = 2 * nint ((hmax - sky_mean) / dh) + 1
nker = 2 * nint (2.0 * (hmax - sky_mean) / (dh * 3.0)) + 1
nsmooth = nbins - nker + 1
dh = (hmax - hmin) / (nbins - 1)
}
kmin = - dh * (nker / 2 + 0.5)
kmax = dh * (nker / 2 + 0.5)
# Test for a valid histogram.
if (nbins < 2 || k1 <= 0.0 || sky_sigma <= 0.0 || dh <= 0.0 ||
sky_sigma <= dh) {
sky_mode = sky_mean
sky_sigma = 0.0
sky_skew = 0.0
return (AP_NOHISTOGRAM)
}
# Allocate space for the histogram and kernel.
call smark (sp)
call salloc (x, nbins, TY_REAL)
call salloc (hgm, nbins, TY_REAL)
call salloc (shgm, nbins, TY_REAL)
call salloc (kernel, nker, TY_REAL)
# Set up x array.
do i = 1, nbins
Memr[x+i-1] = i
call amapr (Memr[x], Memr[x], nbins, 1.0, real (nbins),
hmin + 0.5 * dh, hmax + 0.5 * dh)
# Accumulate the histogram.
call aclrr (Memr[hgm], nbins)
call aclrr (Memr[shgm], nbins)
nsky_reject = nsky_reject + aphigmr (skypix, wgt, index, nskypix,
Memr[hgm], nbins, hmin, hmax)
nsky = nskypix - nsky_reject
# Perform the initial rejection cycle.
if (nsky_reject > 0.0) {
do i = 1, nskypix {
if (wgt[index[i]] <= 0.0) {
dsky = skypix[index[i]] - sky_zero
sumpx = sumpx - dsky
sumsqpx = sumsqpx - dsky ** 2
sumcbpx = sumcbpx - dsky ** 3
}
}
call apmoments (sumpx, sumsqpx, sumcbpx, nsky, sky_zero, sky_mean,
sky_sigma, sky_skew)
}
# Construct kernel and convolve with histogram.
if (sky_sigma > 0.0) {
call ap_gauss_kernel (Memr[kernel], nker, kmin, kmax, sky_sigma)
call acnvr (Memr[hgm], Memr[shgm+nker/2], nsmooth, Memr[kernel],
nker)
} else
call amovr (Memr[hgm], Memr[shgm], nbins)
call ap_corfit (Memr[x], Memr[shgm], nbins, sky_mode, ier)
sky_mode = max (dmin, min (sky_mode, dmax))
if (ier != OK) {
call sfree (sp)
return (ier)
}
if ((IS_INDEFR(losigma) && IS_INDEFR(hisigma)) || (sky_sigma <= dh) ||
maxiter < 1) {
call sfree (sp)
return (AP_OK)
}
# Fit histogram with pixel rejection and optional region growing.
do i = 1, maxiter {
# Compute new histogram limits.
if (IS_INDEFR(losigma))
locut = -MAX_REAL
else
locut = sky_mode - losigma * sky_sigma
if (IS_INDEFR(hisigma))
hicut = MAX_REAL
else
hicut = sky_mode + hisigma * sky_sigma
# Detect rejected pixels.
nreject = 0
do j = 1, nskypix {
if (skypix[index[j]] >= locut && skypix[index[j]] <= hicut)
next
if (rgrow > 0.0)
nreject = nreject + ap_grow_hist2 (skypix, coords,
wgt, nskypix, sky_zero, index[j], snx, sny,
Memr[hgm], nbins, hmin, hmax, rgrow, sumpx, sumsqpx,
sumcbpx)
else if (wgt[index[j]] > 0.0) {
call ap_hgmsub2 (Memr[hgm], nbins, hmin, hmax,
skypix[index[j]], sky_zero, sumpx, sumsqpx, sumcbpx)
wgt[index[j]] = 0.0
nreject = nreject + 1
}
}
if (nreject == 0)
break
# Update the sky parameters.
nsky_reject = nsky_reject + nreject
nsky = nskypix - nsky_reject
if (nsky <= 0)
break
call apmoments (sumpx, sumsqpx, sumcbpx, nsky, sky_zero, sky_mean,
sky_sigma, sky_skew)
if (sky_sigma <= dh)
break
# Recompute the peak of the histogram.
call ap_gauss_kernel (Memr[kernel], nker, kmin, kmax, sky_sigma)
call aclrr (Memr[shgm], nbins)
call acnvr (Memr[hgm], Memr[shgm+nker/2], nsmooth, Memr[kernel],
nker)
call ap_corfit (Memr[x], Memr[shgm], nbins, sky_mode, ier)
sky_mode = max (dmin, min (sky_mode, dmax))
if (ier != AP_OK)
break
}
# Return the appropriate error code.
call sfree (sp)
if (nsky == 0 || nsky_reject == nskypix) {
nsky = 0
nsky_reject = nskypix
sky_mode = INDEFR
sky_sigma = INDEFR
sky_skew = INDEFR
return (AP_NSKY_TOO_SMALL)
} else if (ier != AP_OK) {
sky_mode = sky_mean
sky_sigma = 0.0
sky_skew = 0.0
return (ier)
} else
return (AP_OK)
end
# AP_GAUSS_KERNEL -- Procedure to compute a Gaussian kernel of given length
# and sigma.
procedure ap_gauss_kernel (kernel, nker, kmin, kmax, sky_sigma)
real kernel[ARB] # kernel
int nker # length of kernel
real kmin, kmax # limits of the kernel
real sky_sigma # sigma of the sky
int i
real dk, x, sumx
begin
# Return 1 if unit sized kernel.
if (nker == 1) {
kernel[1] = 1.0
return
}
# Intialize.
sumx = 0.0
x = kmin
dk = (kmax - kmin ) / (nker - 1)
# Compute and normalize the kernel.
do i = 1, nker {
kernel[i] = exp (- (x ** 2) / (2. * sky_sigma ** 2))
sumx = sumx + kernel[i]
x = x + dk
}
do i = 1, nker
kernel[i] = kernel[i] / sumx
end
# AP_CORFIT -- Procedure to compute the peak of the cross-correlation
# function using parabolic interpolation.
procedure ap_corfit (x, shgm, nbins, sky_mode, ier)
real x[ARB] # x coordinates of histogram
real shgm[ARB] # convolved histogram
int nbins # number of histogram bins
real sky_mode # computed sky_mode
int ier # error code
int bin
real max, xo, dh1, dh2
begin
call ap_amaxel (shgm, nbins, max, bin)
if (max <= 0) {
ier = AP_FLAT_HIST
} else if (bin == 1) {
sky_mode = x[1]
ier = AP_OK
} else if (bin == nbins) {
sky_mode = x[nbins]
ier = AP_OK
} else {
xo = 0.5 * (x[bin] + x[bin-1])
dh1 = shgm[bin] - shgm[bin-1]
dh2 = shgm[bin] - shgm[bin+1]
sky_mode = xo + (x[bin] - x[bin-1]) * (dh1 / (dh1 + dh2))
ier = AP_OK
}
end
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