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

[MacQueen, Don]

It would be better to ask this question on r-sig-geo. More people there
are more familiar with the structure of Spatial{*} classes.

-Don

-- 
Don MacQueen

Lawrence Livermore National Laboratory
7000 East Ave., L-627
Livermore, CA 94550
925-423-1062





On 4/8/15, 2:07 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. Š..
>
> 
>
>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 		 	   		  
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