[SciPy-User] interpolate.bispl{rep, ev} need some love, or I'm using them incorrectly...

josef.pktd@gmai... josef.pktd@gmai...
Thu Mar 4 16:10:53 CST 2010


On Thu, Mar 4, 2010 at 4:47 PM, Kurt Smith <kwmsmith@gmail.com> wrote:
> I've been trying to get interpolation working on a not-too-large array
> (512 X 512) using interpolate.interp2d, which is a nice wrapper for
> interpolate.bispl{rep,ev}.  Apparently these routines are meant to
> work on smallish arrays (~ 50 X 50) and give me a segfault when I hand
> them anything about (200 X 200) or so.  When they do work, they're
> prohibitively slow.
>
> My question is:  what is the usecase for these bivariate spline
> routines?  I've discovered ndimage.spline_filter and
> ndimage.map_coordinates -- these fit my purposes much better; fast and
> nice interface.  What is the difference between the two approaches?

>From the docs, I think, bispl is a true 2dim spline, while
ndimage.spline_filter is a sequence of 1d filter applied along each
axis.

For function approximation  200*200=40000  is a large number of points
For  z = f(x,y) I wouldn't usually get as many observations as in an
image, and the number of knot points might be required to be smallish.

I don't know anything about the c or fortran internals of either of them.

Josef

>
> Kurt
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