[GRASS-user] High tension with r.resamp.rst

[Ghislain Vieilledent]

Ciao Nikos,
The pdf is available at the web link provided in the email. Thanks for giving a look.
Cheers,
Ghislain

Le 6 février 2019 15:19:22 GMT+01:00, Nikos Alexandris <nik at nikosalexandris.net> a écrit :
>* Ghislain Vieilledent | CIRAD <ghislain.vieilledent at cirad.fr>
>[2019-02-06 14:11:04 +0100]:
>
>>Dear GRASS GIS user,
>>
>>I am using r.resamp.rst to interpolate climatic data at 30sec 
>>resolution over Africa.
>>
>>Grass script, data, and results are available here:
>>https://nextcloud.fraisedesbois.net/index.php/s/CKzsZCSCqMTY9rq
>>
>>#===================
>>
>># Import Africa shapefile
>>v.in.ogr --overwrite input=gisdata/vectors/Africa layer=Africa
>output=Africa
>>
>># Rasterize Africa at 30 arc-sec resolution
>>g.region -ap vector=Africa res=0:00:30
>>v.to.rast input=Africa type=area output=Africa use=val value=1
>>
>># Import climate
>>r.in.gdal --overwrite input=gisdata/rasters/test1.1_044.tif
>output=test1_1
>>
>># Resample with RST
>>g.region -ap raster=test1_1
>># Note: use maskmap=Africa to save computation time
>>r.resamp.rst --overwrite input=test1_1 elevation=test1_1_rst \\
>>             ew_res=0.00833 ns_res=0.00833 maskmap=Africa
>>r.info test1_1_rst
>>
>># Resample to exact resolution 0:00:30
>>g.region -ap res=0:00:30
>>r.resample --overwrite input=test1_1_rst output=test1_1_30s
>>
>># Export
>>r.out.gdal --overwrite input=test1_1_30s \\
>>             output=output/test1_1_30s.tif type=Float32 \\
>>             createopt='compress=lzw,predictor=2'
>>
>>#===================
>>
>>When I use r.info on the interpolated raster, it indicates a tension 
>>of 7278 in the comments which seems very high to me as the default 
>>value is 40.
>>
>>|   Comments:
>>|    tension=7278.552524
>>|    dnorm=5.495598, zmult=1.000000
>>|    KMAX=50, KMIN=35, errtotal=0.000535
>>|    zmin_data=0.056488, zmax_data=3.756866
>>|    zmin_int=-0.066779, zmax_int=3.214336
>>
>>On the other side, results do not look so bad (see test.pdf figure).
>
>I am following this thread out of curiosity/interest on resampling. 
>The
>.pdf file is not attached.  How big is it?
>
>Nikos
>
>
>>Would you have any comment on this high value for the tension and do 
>>you think interpolation has been performed correctly ?
>>
>>Best regards,
>>
>>Ghislain

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