#98: r.resamp.interp fails for bicubic and bilinear interpolation
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Reporter: cmbarton | Owner: grass-dev@lists.osgeo.org
Type: defect | Status: new
Priority: critical | Milestone: 6.3.0
Component: default | Version: unspecified
Keywords: |
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I just found out that r.resamp.interp fails for both bicubic and bilinear
interpolation. It makes maps with all NAN values. I used the new NC data
set and produced a set of random elevation points (raster and vector),
then tried to use these in r.resamp.interp. The nearest neighbor routine
worked, but the others did not. I tried the original raster point map and
also tried one that I converted to a CELL map. Neither gave usable
results. FWIW, I got the same result using r.bilinear.
I'm having a very difficult time putting together a class on interpolation
using GRASS today. v.surf.bspline does not work, 2 of the 3 methods in
r.resamp.interp do not work. r.bilinear does not work. Pretty bad press.
On Tue, Mar 18, 2008 at 10:01 PM, Helena Mitasova <hmitaso unity.ncsu.edu>
wrote:
> Michael - unless you have at least on point per cell NAN is actually
> a correct result.
> r.resamp.interp is for resampling a raster map not for interpolating
> from randomly distributed points.
> Eg this is the example from the book - you go from 30m resolution to
> 10m resolution -
> let me know if that does not work (then we are in trouble because
> this worked so we may have a bug introduced somewhere).
>
> g.region rast=elevation -p
> r.resamp.interp elev_ned_30m out=elev_ned10m_bil meth=bilinear
> r.resamp.interp elev_ned_30m out=elev_ned10m_bic meth=bicubic
>
> Helena
New documentation wording:
"<EM>r.resamp.interp</EM> resamples an input raster map by interpolating
between
the neighboring cells via a selectable resampling algorithm. All cells
present in the neighborhood of the input raster cell must be non-null to
generate a non-null cell in the output raster map."