[GRASS-dev] Re: another r.resamp.interp bug report

Helena Mitasova hmitaso at unity.ncsu.edu
Wed Mar 19 00:39:41 EDT 2008

Michael - I have added an example from the book at the bottom of this  
page - please try it and let me know whether it works.

Please keep in mind that r.resample* is for reinterpolation of  
continuous data to a different resolution not for interpolation from  
scattered data (see the equations in the Appendix on what it does)   
(r.surf.idw is designed for scattered data input in raster format).  
You should convert your points from raster to vector points and use  
the v.surf* modules to interpolate.

I hope this helps and let me know if the examples don't work

Helena Mitasova
Associate Professor
Department of Marine, Earth
and Atmospheric Sciences
1125 Jordan Hall, Campus Box 8208
North Carolina State University
Raleigh NC 27695-8208

On Mar 19, 2008, at 12:30 AM, Michael Barton wrote:

> On Mar 18, 2008, at 4:06 PM, grass-user-request at lists.osgeo.org wrote:
>> Date: Tue, 18 Mar 2008 20:21:38 +0100
>> From: Nikos Alexandris <nikos.alexandris at felis.uni-freiburg.de>
>> Subject: Re: [GRASS-user] r.in.xyz
>> To: Edmondo Elisei <edmondo.elisei at gmail.com>
>> Cc: grass-user at lists.osgeo.org
>> Message-ID: <1205868098.19886.19.camel at vertical>
>> Content-Type: text/plain
>> On Tue, 2008-03-18 at 17:02 +0100, Edmondo Elisei wrote:
>>> 5) r.bilinear syntax
>>> r.bilinear input=subset output=subsetsurface --overwrite
>> For the second part of the test:
>>  I am having trouble to resample with r.resamp.interp  
>> mode=bilinear. But
>> I think this has to do with the available values (I got only 6 points
>> imported)
>> In the manual one can read as well:
>> Note that for bilinear and bicubic interpolation, cells of the output
>> raster that cannot be bounded by the appropriate number of input cell
>> centers are set to null. This could occur due to the input cells  
>> being
>> outside the current region, being NULL or MASKed.
>> So, I suppose with a larger sample it shoud feasible.
> Nikos,
> I just ran into this today. I haven't done any interpolation in a  
> few months, so I don't know when this bug crept in. I cannot get  
> any decent maps out of r.resamp.interp. The bilinear and bicubic  
> routines only produce NAN maps, and the nearest routine creates a  
> map that is composed only of the input points.
> v.surf.bspline hasn't worked in awhile and I'm getting sporadic  
> crashes (more often than not) with v.surf.rst with no error message  
> (except for a system one that the program has caused an error).
> So for me today, the only interpolation routine that seems to work  
> out of all the ones in the GRASS toolkit is v.surf.idw--one of the  
> worst.
> Michael
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