[R-sig-Geo] create point density raster OR other ways to thin point data

[Robert J. Hijmans]

Julie,

> Any alternative solutions for thinning point data are also appreciated

See:

library(dismo)
?gridSample

Robert

On Sun, Feb 24, 2013 at 10:38 AM, Julie Lee-Yaw <julleeyaw at yahoo.ca> wrote:
> Hi
>
> I have a set of sampling locations with a strong bias towards one area within my study region (e.g. many more points in the south than in the north). I want to "thin" sites in this high density region by randomly discarding sites until the density of sampling is similar to other areas of my study region.
>
> The approach I've come up with so far is something like:
>
> 1) calculate a kernel density or point density raster from the points
> 2) take the average "density value" of all points above (x) and below (y) a user-defined cutoff
> 3) for all points with an initial density value > a defined cutoff, randomly discard point one at a time, create a new density raster, recalculate the average density (x) of these points...repeat until x = y
>
> To make this work, I'm trying to figure out how to produce a kernel density raster or point density raster from point data in R (akin to the "kernel density" and "point density" tools in ArcGIS).
>
> Can anyone point me in the right direction? I have seen the density.ppp function but I am unsure of how to calculate "sigma" or whether this function even what I need to meet my ultimate goal. Any alternative solutions for thinning point data are also appreciated.
>
> _______________________________________________
> R-sig-Geo mailing list
> R-sig-Geo at r-project.org
> https://stat.ethz.ch/mailman/listinfo/r-sig-geo