[R-sig-Geo] subsetting a spatial polygons

[Antonio Silva]

Thanks Michael and Tim, thanks for the attention

The first thing I did was I try the subsets using subset.

subset(polys,
coordinates(polys)[,1]>=-46 & coordinates(polys)[,1]<=-45 &
coordinates(polys)[,2]>=-25 & coordinates(polys)[,2]<=-24)

But it seems to work only with Spatial*DataFrame objects. Then I (unluckily)
gave up the x-y approach.

With Mike's advice I tried again as

plot(
    polys[
        coordinates(polys)[,1]>=-46 & coordinates(polys)[,1]<=-45 &
        coordinates(polys)[,2]>=-25 & coordinates(polys)[,2]<=-24,]
,add=T,col="green")

and I got what I wanted in a more "elegant" fashion.

Once more thanks a lot for the attention.

-- 
Antônio Olinto Ávila da Silva
Instituto de Pesca (Fisheries Institute)
São Paulo, Brasil

Em qua, 12 de set de 2018 às 05:05, Michael Sumner <mdsumner using gmail.com>
escreveu:

> 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
> > >
> >
> > _______________________________________________
> > R-sig-Geo mailing list
> > R-sig-Geo using r-project.org
> > https://stat.ethz.ch/mailman/listinfo/r-sig-geo
> >
> --
> Dr. Michael Sumner
> Software and Database Engineer
> Australian Antarctic Division
> 203 Channel Highway
> Kingston Tasmania 7050 Australia
>
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>
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