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Interpolation Package
The routines here are intended to allow programmers to interpolate
one dimensional arrays and two dimensional
images in the IRAF system. The routines are
mathematical in nature and are not heavily tied into the IRAF package.
The advantages of having locally written interpolators include the
ability to optimize for uniformly spaced data and the possibility of
adding features that are useful for the final application. The
one major feature that has been implemented is the ability to change
the kind of interpolator used at run time by carrying along a variable
that gives the interpolator type in the higher level code.
The kinds of interpolators include:
1. Nearest neighbor
2. Linear
3. Interior polynomial order = 3
4 Interior polynomial order = 5
5 Spline order = 3
The package is divided into array interpolators and image
interpolators. Within the array interpolators, there is further
division into sequential and random interpolators. The sequential
interpolators are optimized for returning many values as is the
case when an array is shifted or when an array is oversampled
at many points in order to produce a smooth plot. The random interpolators
allow the evaluation of a few interpolated points without the computing
time and storage overhead required for setting up the sequential version.
The original specification called for the interpolator package
to deal with indefinite valued pixels and references out of bounds.
A version of the array sequential interpolators was written that handled
both situations allowing some options to the user. The extension of
these features to the two dimensional case becomes more dependent on
details within IRAF and less mathematical in nature. It would also
duplicate other code within IRAF that deals with out of bound references.
Finally the need to test for the various situations slows down the operation.
So all features referring to indefinite valued pixels and out of bound
references have been removed. The user is responsible for ensuring that
"x" values land within the array. The code does not test to see if x
is in bounds. A routine has been added that interpolates
an array with indefinites and returns an array with all legitimate
real numbers.
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