[R] extracting slot "coords" from a Polygons class object

[Michael Sumner]

Note that you can get everything (without recording its structure) with
coordinates(as(as(x, "SpatialLines"), "SpatialPoints")) - also  ggplot2
uses fortify methods to turn these objects into tables.

Cheers, Mike.

On Thu, 9 Apr 2015 at 22:57 Monica Pisica <pisicandru at hotmail.com> wrote:

> Hi Sarah,
>
>
> Thank you so much. This is exactly what i need it. I was wondering if my
> parsing was totally wrong. I read the SpatialPolygons-class help, but
> obviously i didn't understand it.
>
>
> Again, thanks so much,
>
>
> Monica
>
> ----------------------------------------
> > Date: Wed, 8 Apr 2015 20:42:56 -0400
> > Subject: Re: [R] extracting slot "coords" from a Polygons class object
> > From: sarah.goslee at gmail.com
> > To: pisicandru at hotmail.com
> > CC: r-help at r-project.org
> >
> > You didn't parse the output you pasted in correctly:
> >
> > pt1.cpoly at polygons[[1]]@Polygons[[1]]@coords
> >
> > or
> >
> > coordinates(pt1.cpoly at polygons[[1]]@Polygons[[1]])
> >
> >> class(pt1.cpoly)
> > [1] "SpatialPolygons"
> > attr(,"package")
> > [1] "sp"
> >
> > So see
> > ?"SpatialPolygons-class"
> > for details.
> >
> > Sarah
> >
> > On Wed, Apr 8, 2015 at 5:07 PM, Monica Pisica <pisicandru at hotmail.com>
> wrote:
> >>
> >> Hi,
> >>
> >>
> >>
> >> I am struggling to extract the polygon vertices from a list of an
> object class "Polygons", specifically the slot "coords".
> >>
> >>
> >>
> >> I have a point, and i "draw" a buffer around with gBuffer, i am
> "extracting" the polygon form the SpatialPolygons class and i end up with a
> list of 1 one object Polygons class that seems to have slots, but if i try
> to extract them i get an error.
> >>
> >>
> >>
> >> So here it goes after i load the respective libraries: sp, maptools,
> rgdal, rgeos
> >>
> >> pt1 <- data.frame(x=217680.2, y = 3817555)
> >>
> >> coordinates(pt1) <- c("x", "y")
> >>
> >> crs = "+proj=utm +zone=11 +datum=NAD83 +units=m +no_defs +ellps=GRS80
> +towgs84=0,0,0"
> >>
> >>
> >>
> >> proj4string(pt1) <- CRS(crs)
> >>
> >> pt1.cpoly <- gBuffer(pt1, width = 100, byid = TRUE)
> >>
> >>
> >>
> >> pt1.cpoly
> >>
> >> class : SpatialPolygons
> >>
> >> features : 1
> >>
> >> extent : 217580.2, 217780.2, 3817455, 3817655 (xmin, xmax, ymin, ymax)
> >>
> >> coord. ref. : +proj=utm +zone=11 +datum=NAD83 +units=m +no_defs
> +ellps=GRS80 +towgs84=0,0,0
> >>
> >>
> >>
> >> pt1.poly <- pt1.cpoly at polygons
> >>
> >>
> >>
> >> pt1.poly
> >>
> >> [[1]]
> >>
> >> An object of class "Polygons"
> >>
> >> Slot "Polygons":
> >>
> >> [[1]]
> >>
> >> An object of class "Polygon"
> >>
> >> Slot "labpt":
> >>
> >> [1] 217680.2 3817554.7
> >>
> >>
> >>
> >> Slot "area":
> >>
> >> [1] 30901.7
> >>
> >>
> >>
> >> Slot "hole":
> >>
> >> [1] FALSE
> >>
> >>
> >>
> >> Slot "ringDir":
> >>
> >> [1] 1
> >>
> >>
> >>
> >> Slot "coords":
> >>
> >> x y
> >>
> >> [1,] 217780.2 3817555
> >>
> >> [2,] 217775.3 3817524
> >>
> >> [3,] 217761.1 3817496
> >>
> >> [4,] 217739.0 3817474
> >>
> >> Etc. …..
> >>
> >>
> >>
> >> pt1.crd <- pt1.poly[[1]]@coords
> >>
> >> Error: no slot of name "coords" for this object of class "Polygons"
> >>
> >>
> >>
> >> So my question is: How do i access the "coords" slot i clearly see when
> i print pt1.poly on the screen?
> >>
> >>
> >>
> >> Thanks for any help,
> >>
> >>
> >>
> >> Monica
> >> ______________________________________________
> >> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> >> https://stat.ethz.ch/mailman/listinfo/r-help
> >> PLEASE do read the posting guide http://www.R-project.org/posti
> ng-guide.html
> >> and provide commented, minimal, self-contained, reproducible code.
> >
> >
> >
> > --
> > Sarah Goslee
> > http://www.functionaldiversity.org
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posti
> ng-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

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