[R-sig-eco] spatial/mapping question

[Marcelino de la Cruz]

Hi Matt

You can play with spatstat.

You only need to convert your polygon into a "owin" object (see the 
vignette about importing shapefiles in spatstat if necessary) and then 
use functions gridcenters and inside.owin

For example

library(spatstat)

# this is an irregular "window" (aka owin object)
plot(letterR)

# make your regular grid
mygrid<-gridcenters(letterR, nx=10, ny=10)

# plot it

points(mygrid)

# which ones are inside the polygon?

points(as.data.frame(mygrid)[inside.owin(mygrid, w=letterR),], pch=19)
as.data.frame(mygrid)[inside.owin(mygrid, w=letterR),]



HTH,

Marcelino
El 29/05/2013 18:44, Matthew Forister escribió:
> Hi folks,
>
> I need to perform a certain map-based task in R, and I'm hoping that
> someone can point me towards the right package or approach:
>
> I have lat/long coordinates that specify the corners of a polygon, and I
> need to be able to draw a grid within that polygon where the points of the
> grid are regularly spaced at intervals I determine.  Then I want to extract
> that list of points from the grid (so that I can send people out to take
> samples at those grid points).
>
> I've been looking around, and the closet thing I've seen is map.grid
> {mapproj}, which seems to be restricted to a shape defined by 4 points
> rather than a many-sided polygon which is what I need....
>
> Any pointers would be very welcome!
> thanks
> Matt
>
>