.help msigrl Dec98 "Image Interpolation Package"
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NAME
msigrl -- integrate the interpolant inside a polygon 
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SYNOPSIS
y = msigrl (msi, x, y, npts)

.nf
    pointer	msi		#I interpolant descriptor
    real	x[npts]		#I x values, 1 <= x <= npts, x[1] = x[npts]
    real	y[npts]		#I y values, 1 <= y <= npts, y[1] = y[npts]
    int		npts		#I number of points
.fi
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ARGUMENTS
.ls msi    
Pointer to the sequential interpolant descriptor structure.
.le
.ls x, y
An array of x and y values describing a polygon, where x[1] = x[npts] and
y[1] = y[npts]. X and y describe a closed curve where any horizontal line
segment intersects the domain of integration at at most one point.
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.ls npts
The number of points describing the polygon. Npts must >= 4 (triangle).
.le
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DESCRIPTION
MSIGRL integrates the interpolant exactly for rectangular domains
of integration. For more irregular regions of integration MSIGRL
returns an approximation whose accuracy depends on the size of the
integration region and the shape of the polygon.
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NOTES
Checking for out of bound integration regimes is the responsibility of
the user. Non-rectangular partial pixel domains of integration default
to rectangular regions.  MSIINIT or MSISINIT and MSIFIT must be called
before using MSIGRL.
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SEE ALSO
msisqrgl
.endhelp