extracting slot "coords" from a Polygons class object

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

ng-guide.html

--
Sarah Goslee
http://www.functionaldiversity.org