[GRASS-dev] [GRASS GIS] #99: r.resamp.interp fails for bicubic and bilinear interpolation

Helena Mitasova hmitaso at unity.ncsu.edu
Tue Mar 18 17:01:24 EDT 2008

On Mar 18, 2008, at 2:39 PM, GRASS GIS wrote:

> #99: r.resamp.interp fails for bicubic and bilinear interpolation
> ---------------------- 
> +-----------------------------------------------------
>  Reporter:  cmbarton  |       Owner:  grass-dev at lists.osgeo.org
>      Type:  defect    |      Status:  new
>  Priority:  critical  |   Milestone:  6.3.0
> Component:  default   |     Version:  unspecified
>  Keywords:            |
> ---------------------- 
> +-----------------------------------------------------
>  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.

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


> 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.
>  Michael
> -- 
> Ticket URL: <http://trac.osgeo.org/grass/ticket/99>
> GRASS GIS <http://grass.osgeo.org>
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