[R] extracting coordinates from SpatialPolygonsDataFrame using slot functions

[Paul Hiemstra]

Jeff Hamann wrote:
> In converting some older code:
>
> ## builds an OWIN to generate a set of points on a grid within the OWIN object:
> bdry <- read.shape( "../../data/boundary.shp" )
> outline.verts <- bdry$Shapes[[2]]$verts[1:bdry$Shapes[[2]]$Pstart[2],]
> outline.order <- nrow( outline.verts ) : 2
> bdry.poly <- vector( 2, mode="list" )
> bdry.poly[[1]] <- list( x=outline.verts[outline.order,1], 
>                   y=outline.verts[outline.order,2] )
> bdry.poly[[2]] <- list( x=bdry$Shapes[[1]]$verts[1:(nrow(bdry$Shapes[[1]]$verts)-1),1], 
>                    y=bdry$Shapes[[1]]$verts[1:(nrow(bdry$Shapes[[1]]$verts)-1),2] )
> bdry.owin <- owin( poly=bdry.poly )
> grid <- gridcentres( bdry.owin, 200, 200 ) 
>
> I've run across the following problem where I now need to use the readShapePoly function in the sp package:
>
> bdry2 <- readShapePoly( "../../data/boundary.shp" )
>
> which requires the elements be accessed using the slot function? 
>
> My question, after trying to find the answer on-line and in some docs, is how?
>
> Help?
>
> Also, I'm not sure I get the r-help digests, so if someone can shed light on the subject, can you please respond directly?
>
> ______________________________________________
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>   
Hi,

A good way to get coordinates of a SPDF is to use the fortify function 
from ggplot2. It is mainly used to be able to plot the polygons in 
ggplot, but it also serves to get the coodinates into a data.frame very 
nicely. See:

http://www.mail-archive.com/r-sig-geo@stat.math.ethz.ch/msg07522.html

For more details.

cheers,
Paul

ps The r-sig-geo list migh get you more response than R-help.

-- 
Drs. Paul Hiemstra
Department of Physical Geography
Faculty of Geosciences
University of Utrecht
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3508 TC Utrecht
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Phone:  +3130 253 5773 Wed-Fri
http://intamap.geo.uu.nl/~paul
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