interpolate.bispl{rep, ev} need some love, or I'm using them incorrectly...
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? Kurt
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
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On Thu, Mar 4, 2010 at 4:10 PM, <josef.pktd@gmail.com> wrote:
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.
Thanks. It looks like interpolate.bisplrep is suitable for irregularly spaced data, whereas ndimage.spline_filter & map_coordinates require gridded data (naturally, since they're used on image-like data).
Josef
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