Interpolation option: IDW or OK?
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: r-sig-geo-bounces at stat.math.ethz.ch
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https://stat.ethz.ch/mailman/listinfo/r-sig-geo or, via email, send a message with subject or body 'help' to r-sig-geo-request at stat.math.ethz.ch You can reach the person managing the list at r-sig-geo-owner at stat.math.ethz.ch When replying, please edit your Subject line so it is more specific 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 <aloboaleu at gmail.com> Subject: [R-sig-Geo] error rgdal library if used from within Grass plugin (Windows) To: r-sig-geo at stat.math.ethz.ch Message-ID: <49903860.8060406 at gmail.com> 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 M?nster Weseler Stra?e 253, 48151 M?nster, Germany. Phone: +49 251 8333081, Fax: +49 251 8339763 http://ifgi.uni-muenster.de/ http://www.springer.com/978-0-387-78170-9 e.pebesma at wwu.de