Dear all, I am interpolating automatically daily air temperature values using kriging with external drift (altitude) and the library gstat. From time to time (quite random) I get unrealistic predictions like -400?C with very high kriging weights like 2000. Looking at the data everything seems to be ok. Then I changed the variogram ranges a little bit and the problem disappears. How can this behavior be explained? I have attached a small example script for demonstration and some data. Thanks you Tobias -------------- next part -------------- A non-text attachment was scrubbed... Name: example.R Type: application/x-extension-r Size: 1236 bytes Desc: not available URL: <https://stat.ethz.ch/pipermail/r-sig-geo/attachments/20130702/1290aff5/attachment.bin> -------------- next part -------------- A non-text attachment was scrubbed... Name: points2.Data Type: application/octet-stream Size: 865 bytes Desc: not available URL: <https://stat.ethz.ch/pipermail/r-sig-geo/attachments/20130702/1290aff5/attachment.obj> -------------- next part -------------- A non-text attachment was scrubbed... Name: mypoint.Data Type: application/octet-stream Size: 343 bytes Desc: not available URL: <https://stat.ethz.ch/pipermail/r-sig-geo/attachments/20130702/1290aff5/attachment-0001.obj>
Huge kriging weights when using kriging with external drift in gstat
4 messages · Tobias Vetter, Edzer Pebesma
Tobias, try using another variogram model: the linear model with sill is not positive definite in more than one dimension (and yes: a warning about this would have been very nice!)
On 07/02/2013 03:37 PM, Tobias Vetter wrote:
Dear all, I am interpolating automatically daily air temperature values using kriging with external drift (altitude) and the library gstat. From time to time (quite random) I get unrealistic predictions like -400?C with very high kriging weights like 2000. Looking at the data everything seems to be ok. Then I changed the variogram ranges a little bit and the problem disappears. How can this behavior be explained? I have attached a small example script for demonstration and some data. Thanks you Tobias
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Edzer Pebesma Institute for Geoinformatics (ifgi), University of M?nster Weseler Stra?e 253, 48151 M?nster, Germany. Phone: +49 251 83 33081, Fax: +49 251 8339763 http://ifgi.uni-muenster.de
Thank you. So as long as all my distances are smaller than the range I will not have this problem? Tobias
Tobias, try using another variogram model: the linear model with sill is not positive definite in more than one dimension (and yes: a warning about this would have been very nice!) On 07/02/2013 03:37 PM, Tobias Vetter wrote:
Dear all, I am interpolating automatically daily air temperature values using kriging with external drift (altitude) and the library gstat. From time to time (quite random) I get unrealistic predictions like -400?C with very high kriging weights like 2000. Looking at the data everything seems to be ok. Then I changed the variogram ranges a little bit and the problem disappears. How can this behavior be explained? I have attached a small example script for demonstration and some data. Thanks you Tobias
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Right, I believe the linear model without sill -- vgm(1, "Lin", 0) -- does work; note that the 1 in this case is a slope, no longer a partial sill. You may also set the range to a value larger than the maximum possible distance.
On 07/02/2013 04:16 PM, Tobias Vetter wrote:
Thank you. So as long as all my distances are smaller than the range I will not have this problem? Tobias
Tobias, try using another variogram model: the linear model with sill is not positive definite in more than one dimension (and yes: a warning about this would have been very nice!) On 07/02/2013 03:37 PM, Tobias Vetter wrote:
Dear all, I am interpolating automatically daily air temperature values using kriging with external drift (altitude) and the library gstat. From time to time (quite random) I get unrealistic predictions like -400?C with very high kriging weights like 2000. Looking at the data everything seems to be ok. Then I changed the variogram ranges a little bit and the problem disappears. How can this behavior be explained? I have attached a small example script for demonstration and some data. Thanks you Tobias
_______________________________________________ R-sig-Geo mailing list R-sig-Geo at r-project.org https://stat.ethz.ch/mailman/listinfo/r-sig-geo
_______________________________________________ R-sig-Geo mailing list R-sig-Geo at r-project.org https://stat.ethz.ch/mailman/listinfo/r-sig-geo
Edzer Pebesma Institute for Geoinformatics (ifgi), University of M?nster Weseler Stra?e 253, 48151 M?nster, Germany. Phone: +49 251 83 33081, Fax: +49 251 8339763 http://ifgi.uni-muenster.de