[R-sig-Geo] Is it possible to calculate the semivariances of a variogram between one specific point and all other points in space?

[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]]
> 
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-- 
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.52north.org/geostatistics      e.pebesma at wwu.de