I can think of two reasons, without having looked at anything else than
your message:
1. Range=162 may mean a different thing for the exponential model; for
gstat it means the range parameter as in c1(1-exp(h/a)). This is all
documented. In ArcGIS it might mean something like c1(1-exp(h/(3a)); for
you the responsibility to verify this.
2. setting nmax does not necessarly lead to uniquely defined
neighbourhoods; think of data on a grid.
I understand and do recognize your worries. gstat has been in the open
source for over 10 years now; before you spread fear, uncertainty and
doubt I would have appreciated it if you had kept your observations and
questions directed to this list more factual, and reproducable/verifiable.
Also note that gstat allows YOU to double check the underlying
algorithms; this in contrast to the other software you mention. You're
suggesting now to 1000+ subscribers that this burden lies with me, and
worse, that I didn't do this.
--
Edzer
Yong Li wrote:
Hi Edzer,
I found a problem with gstat "krige" prediction if I am correct this
time. For example, with OLSENP variable in my dataset, I developed a
theoretical model for log(OLSENP) variogram: model=exp, c0=0.2019,
c1=0.2218 and Range=162 meters. By using this model, I predicted the
OLSENP surface using gstat krige and ArcGIS Spatial Analyst with the
same nmax and found the results are significantly different. gstat
significantly underestimated values (here is where I had an idea to use
IDW), but Spatial Analyst gave very reliable predictions. I would like
you to double check the algorithms behind gstat.
By the way, I start to puzzle because I used gstat to calculate other
variables in my dataset, such as total nitrogen and extractable
potassium and also I used gstat to run a series regression-kriging to
predict soil organic matter distribution and submitted to a journal
already.
I appreciate you could give me your response as soon as possible.
Regards
Yong Li
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of
[email protected]
Sent: Tuesday, 10 February 2009 10:00 PM
To: [email protected]
Subject: R-sig-Geo Digest, Vol 66, Issue 10
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than "Re: Contents of R-sig-Geo digest..."
Today's Topics:
1. error rgdal library if used from within Grass plugin
(Windows) (Agustin Lobo)
2. Re: error rgdal library if used from within Grass plugin
(Windows) (Roger Bivand)
3. Re: FW: Interpolcation option: IDW or OK? (Tomislav Hengl)
4. Calculating descriptive stats from many maps (Rainer M Krug)
5. Re: Calculating descriptive stats from many maps (Tomislav Hengl)
6. Re: Calculating descriptive stats from many maps (Roger Bivand)
7. Interpolcation option: IDW or OK? (Yong Li)
8. Re: Calculating descriptive stats from many maps (Robert Hijmans)
9. Re: FW: Interpolcation option: IDW or OK? (Robert Hijmans)
10. Re: Calculating descriptive stats from many maps (Rainer M Krug)
----------------------------------------------------------------------
Message: 1
Date: Mon, 09 Feb 2009 15:06:24 +0100
From: Agustin Lobo <[email protected]>
Subject: [R-sig-Geo] error rgdal library if used from within Grass
plugin (Windows)
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=iso-8859-1; format=flowed
Hi!
The following error only occurs if the R (2.7.2) session is started
from a GRASS shell opened through the QGIS GRASS plugin in windows.
The error does not occur If R is started form its own icon
or by double click in the .RData object, but then the spgrass6
package would not find the GRASS environment.
It also works in linux.
The involved commands are:
1. Start QGIS
2. Star GRASS plugin and open mapset
3. Open Grass Shell
4. Run R and execute require(spgrass6)
Loading required package: spgrass6
Loading required package: sp
Loading required package: rgdal
Error in fun(...) :
GDAL Error 1: Can't load requested DLL:
C:\OSGeo4W\bin\gdalplugins\gdal_ECW_JP2ECW.dll
126: N?o foi poss?vel encontrar o m?dulo especificado.
Error : .onLoad failed in 'loadNamespace' for 'rgdal'
Erro: package 'rgdal' could not be loaded
Any help appreciated.
Agus
--
Edzer Pebesma
Institute for Geoinformatics (ifgi), University of Münster
Weseler Straße 253, 48151 Münster, Germany. Phone: +49 251
8333081, Fax: +49 251 8339763 http://ifgi.uni-muenster.de/
http://www.springer.com/978-0-387-78170-9 [email protected]
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