[R-sig-Geo] subsetting a spatial polygons

[Michael Sumner]

crop doesn't select it actually cuts on the boundary, for simple shapes I
use coordinates (for centroids in easy matrix) and select with [ using
tests on x and y.

Cheers, Mike

On Wed, Sep 12, 2018, 15:29 Tim Appelhans <tim.appelhans using gmail.com> wrote:

> Antonio,
>
> I am not sure why you think that your solution is not very elegant.
> In case you want to have more visual control over the subsetting, you
> could try mapedit:
>
> library(mapedit)
> myselection = selectFeatures(polys, mode = "draw")
>
> which will let you draw a e.g. rectangle and only return those features
> that intersect it.
>
> Best
> Tim
>
>
> On 09/12/2018 04:18 AM, Antonio Silva wrote:
> > Dear list users
> >
> > I have a SpatialPolygons with several squares. How to subset it to have
> > only the squares between given latitudes and longitudes?
> >
> > In the example
> >
> > library(sp)
> > library(raster)
> > grd <-
> >
> GridTopology(cellcentre.offset=c(-47.75,-25.416667),cellsize=c(10/60,10/60),cells.dim=c(23,12))
> > polys <- as.SpatialPolygons.GridTopology(grd)
> > proj4string(polys) <- CRS("+proj=longlat +datum=WGS84")
> > plot(polys,axes=T)
> >
> > How to select only the squares, let's say, between 24-25°S and 45-46°W?
> >
> > The farthest I went was:
> >
> > e <- extent(-45.9,-45.1,-24.9,-24.1) # which is not very elegant
> > mask <- crop(polys,e)
> > polys2 <- polys[mask,]
> > plot(polys2,add=T,col="green")
> >
> > Thanks a lot. Best regards
> >
>
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-- 
Dr. Michael Sumner
Software and Database Engineer
Australian Antarctic Division
203 Channel Highway
Kingston Tasmania 7050 Australia

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