[R-sig-Geo] Efficient way to obtain gridded count of overlapping polygons?

[Lyndon Estes]

Hi Robert,

Many thanks for that suggestion as well, I appreciate it, which also
does the trick.

Just to update the time differences between the 3 methods, in case
anyone else is interested:

Function I wrote: 2.07 seconds
The "over" method from Edzer: 0.612 seconds
Rasterize function: 5.61 seconds (line of code used is below)


r2 <- rasterize(sppX3, r, fun = "count")

r was created from a shape of Africa with 1 degree resolution

Thanks again, Lyndon

On Thu, Feb 17, 2011 at 11:48 AM, Robert Hijmans <r.hijmans at gmail.com> wrote:
>
>> I am interested in creating a raster that summarizes the number of
>> overlapping polygons that underlie each cell (in order to display how
>> many species occur at that point).
>
> Lyndon,
>
> You can also do the below, with raster, see ?rasterize:
>
> r <- rasterize(pols, r, fun='count')
>
> or
>
> r <- rasterize(pols, r, fun=function(x,...)length(na.omit(x)))
>
>
> --
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>
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-- 
Lyndon Estes
Research Associate
Woodrow Wilson School
Princeton University
+1-609-258-2392 (o)
+1-609-258-6082 (f)
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lestes at princeton.edu