An embedded and charset-unspecified text was scrubbed... Name: not available URL: <https://stat.ethz.ch/pipermail/r-sig-geo/attachments/20120907/3c6646a9/attachment.pl>
Is it possible to calculate the semivariances of a variogram between one specific point and all other points in space?
2 messages · Laura Wette, Edzer Pebesma
The variogram cloud might be what you're looking for. In the output table, all individual point pairs (up to some spatial separation distance) are reported, and identified by columns "left" and "right". Selecting a point (last example) needs coercion to data.frame first.
library(gstat)
Loading required package: sp
Loading required package: spacetime
Loading required package: zoo
Attaching package: ?zoo?
The following object(s) are masked from ?package:base?:
as.Date, as.Date.numeric
Loading required package: xts
loadMeuse() v = variogram(log(zinc)~1, meuse, cloud=TRUE) v[1:10,]
dist gamma dir.hor dir.ver id left right 1 70.83784 0.006065804 0 0 var1 2 1 2 118.84864 0.109534743 0 0 var1 3 1 3 141.56624 0.167153095 0 0 var1 3 2 4 259.23927 0.952808244 0 0 var1 4 1 5 282.85155 1.110920725 0 0 var1 4 2 6 143.17123 0.416229664 0 0 var1 4 3 7 366.31407 0.890852716 0 0 var1 5 1 8 362.64032 1.043938763 0 0 var1 5 2 9 251.02390 0.375633672 0 0 var1 5 3 10 154.26276 0.001041290 0 0 var1 5 4
plot(v) vdf = as.data.frame(v) vdf[vdf$right == 1,][1:10,]
dist gamma dir.hor dir.ver id left right 1 70.83784 0.006065804 0 0 var1 2 1 2 118.84864 0.109534743 0 0 var1 3 1 4 259.23927 0.952808244 0 0 var1 4 1 7 366.31407 0.890852716 0 0 var1 5 1 11 473.62960 0.833549786 0 0 var1 6 1 16 258.32151 0.586528972 0 0 var1 7 1 22 252.04960 0.426115526 0 0 var1 8 1 29 380.18943 0.583407369 0 0 var1 9 1 37 471.00849 1.479252663 0 0 var1 10 1 46 510.07548 1.424283374 0 0 var1 11 1
On 09/07/2012 11:52 AM, Laura Wette wrote:
Hello all, I searched the internet very long for an answer, but didn't find one, so I hope you can help me. I have to test several study sites for representativeness for the environment and therefore I have remotely sensed raster data, which reproduce the NDVI (Normalized Differenced Vegetation Index). The pixel values vary between -1 and 1. I've also got the coordinates of the study sites' centers and all the coordinates for all pixels and their values. For this purpose I decided to calculate variograms for the study sites and their environment with the variog()-function of the geoR-Package. Unfortunately, with this function it is only possible to calculate the semi-variances for each pair of points in the investigated area and not for pairs of one specific point and any other point (if I understood the R Documentation correctly). So the calculated semi-variances have nothing to do with study sites, as they have no spatial connection. Could you please tell me, if it is possible to calculate these variograms with a given starting point? I.e. is it possible to calculate the semivariances between one specific point( the "starting point", which is one study site) and all other points (the environment of the study sites), which are located in different distances? Is it possible to do so with variog() or do have to calculate with other packages like gstat, spatial or nlme? In the gstat-manual (www.gstat.org/gstat.pdf) I found a so-called local neighbourhood selection. Is there anything similar available for the geoR package? If not, how can I implement the commands in the variogram()-function of the gstat-package? Can I use this local neighbourhood selection at all or is it a wrong aprroach? Thank you very much for any answer! Laura [[alternative HTML version deleted]]
_______________________________________________ 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 8333081, Fax: +49 251 8339763 http://ifgi.uni-muenster.de http://www.52north.org/geostatistics e.pebesma at wwu.de