.help msieval Dec98 "Image Interpolation Package"
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NAME
msieval -- procedure to evaluate the interpolant at x and y
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SYNOPSIS
z = msieval (msi, x, y)

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pointer		msi		#I interpolant descriptor
real		x[4]		#I x value, 1 <= x[1-4] <= nxpix
real		y[4]		#I y value, 1 <= y[1-4] <= nypix
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ARGUMENTS
.ls msi    
The pointer to the sequential interpolant descriptor structure.
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.ls x, y
The single x and y values of or in the case of the drizzle interpolant
the single quadrilateral over which the point is to be evaluated.
.le
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DESCRIPTION
The polynomial coefficients are calculated from the data points in the
case of the polynomial interpolants and the B-spline coefficients in
the case of the spline interpolant. The polynomial interpolants
are evaluated using Everett's central difference formula. The boundary
extension algorithm is projection.

The sinc interpolant is evaluated using an array of data points around
the desired position. The look-up table sinc interpolant is computed
using an a pre-computed look--up table entry. The boundary extension
algorithm is nerest neighbor.

The drizzle interpolant is computed by computing the mean value of the
data within the user supplied quadrilateral.
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NOTES
Checking for out of bounds and INDEF valued pixels is the responsibility of
the user. MSIINIT or MSISINIT and MSIFIT must be called before calling
MSIEVAL.
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SEE ALSO
msivector, mrieval, mrider
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