From: Michael Fuller <mmfuller_at_tiem.utk.edu>

Date: Sat 03 Jun 2006 - 04:54:46 EST

etc

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Received on Sat Jun 03 05:02:06 2006

Date: Sat 03 Jun 2006 - 04:54:46 EST

I'm using R for Mac OSX version 1.14 (2129) and the geoR package
version 1.6-5 (the current version in the R repository). I'm running
R in OS 10.4.6 on a Mac G4 iBook (933MHz, 640 MB DDR SDRAM). I
searched the R archive and did not find a posting on this issue.

I want to use the variog and variog4 functions of geoR to characterize the pattern of spatial autocorrelation of tree density on a forest plot. But I get incomplete line plots when I plot the output of variog4, compared to the plot for the output of variog. I'm using the same geodata for each plot.

I've attached 2 graphs to illustrate. The first is a plot of a 90-
degree directional variogram created using variog:

> trees90.vgm<-variog(trees.geo,max.dist=100,direction=pi/2)

> plot(trees90.vgm)

The second is a plot of a multidirectional variogram created using
variog4:

> trees.vgm4<-variog4(trees.geo,max.dist=100)

> plot(trees.vgm4)

The graphs are also available at:

www.tiem.utk.edu/~mmfuller/R_plots.pdf

You can see that the 90 degree line in the multi-line plot from variog4 (dotted green line) does not include all the data shown in the single 90 degree variogram (circles) plotted using variog. The lines for other directions in the variog4 plot are also incompletely drawn.

Any suggestions as to what's causing this plotting problem?

The raw data is a file containing 3 columns x,y,z. The x,y values are the coordinates of quadrats placed end to end in a grid on a forest plot. The z values are the density of trees in each quadrat. Each quadrat is 15m square and the plot dimensions are 220x780m. The data are arranged in columns (coordinates 20 to 240) and rows (coordiantes 765 to 150) representing the data posting of each quadrat.

I create geodata objects using:

trees.geo<-read.geodata("tree.dat",header=TRUE)

Here is a data sample:

x y z 20 765 0.1556 35 765 0.1556 50 765 0.0356 65 765 0.0622 80 765 0.0933 95 765 0.0400 110 765 0.1111 125 765 0.1244 140 765 0.0800 155 765 0.0667 170 765 0.0711 185 765 0.0889 200 765 0.0667 215 765 0.0844 20 750 0.1067 35 750 0.0800 50 750 0.0578 65 750 0.0622 80 750 0.0578 95 750 0.0933 110 750 0.0844 125 750 0.1200 140 750 0.0711 155 750 0.0711 170 750 0.0711 185 750 0.0578 200 750 0.0489 215 750 0.0933

etc

I have repeated the analysis using different quadrat sizes and the problem of incomplete drawing of lines is unaffected.

Any suggestions are appreciated!

Mike

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- application/pdf attachment: trees.vgm4.pdf

- application/pdf attachment: trees90.vgm.pdf

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