6

I want to perform cell declustering in a small point data set.

I have 9 observation points and I want to find the size of the region of influence for an observation, and afterwards use that as weight in analysis.

The only way, I could find is that one:

library('gstat')
library('sp')
data(meuse)
coordinates(meuse) = ~x + y 
data(meuse.grid)
coordinates(meuse.grid) = ~x + y 
gridded(meuse.grid) <- TRUE

zn.tp = krige(log(zinc) ~ 1, meuse, meuse.grid, nmax = 1) 
image(zn.tp["var1.pred"]) 
points(meuse, pch = "+", cex = 0.65) 
cc = coordinates(meuse) 
library(tripack)
plot(voronoi.mosaic(cc[, 1], cc[, 2]), do.points = FALSE, add = TRUE)
title("Thiessen (or Voronoi) polygon interpolation of log(zinc)")

enter image description here

So, after preparing the data, I could create Thiessen (Voronoi) polygons. However, It works properly only when I made decision about the borders of my grid.

How I could perform cell declustering, that will also take care of creating the outer borders?


The only idea I could find was DECLUST function from gslib http://www.statios.com/help/declus.html . Could cell declustering be done in less difficult way?

1
+50

Nine points is a quite small number, so I would use some arbitrary boundary instead of trying to build a complex algorithm that might "go wild".

I suggest that you use r.grow.distance in grass to create a distance layer around your points, and to set a threshold that would constraint the size of your study area (for instance, the largest distance value between two pairs of neighbour points). then you can crop your thiessen polygons.

As a remark, you could do the same (buffer + dissolve buffer) or similar (convex hull + buffer) with vectors in QGIS.

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