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.help asieval Dec98 "Image Interpolator Package"
.ih
NAME
asieval -- procedure to evaluate interpolant at x
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SYNOPSIS
y = asieval (asi, x)
.nf
pointer asi #I interpolant descriptor
real x[2] #I x value, 1 <= x[1-2] <= npts
.fi
.ih
ARGUMENTS
.ls asi
Pointer to the sequential interpolant descriptor structure.
.le
.ls x
Single X value, or pair of X values defining a range in the case of the
drizzle interpolant.
.le
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DESCRIPTION
The polynomial coefficients are calculated directly from the data points
for the polynomial interpolants, and from the B-spline coefficients for
the cubic spline interpolant. The actual calculation is done by adding and
multiplying terms according to Everett's central difference interpolation
formula. The boundary extension algorithm is projection.
The sinc interpolant is computed using a range of data points around
the desired position. Look-up table sinc interpolation is computed
using the most appropriate entry in a precomputed look-up table.
The boundary extension algorithm is nearest neighbor.
The drizzle interpolant is computed by summing the data over the user
supplied X interval.
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NOTES
Checking for out of bounds and INDEF valued pixels is the responsibility of
the user. ASIINIT or ASISINIT and ASIFIT must be called before using ASIEVAL.
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SEE ALSO
asivector, arieval
.endhelp
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