[R-sig-Geo] extracting polygons

[Andrew Niccolai]

Try this code from my dataset:

## Read in var crown circular model
crown.shp <-
"C:/Niccolai/01_PhD/Papers/Paper003/GIS_LAYERS/CB_CRLOCS_ADJ_ALL_PREDINT99_B
uffer.shp"
crown.poly <- readShapePoly(crown.shp)
crown.data <-
read.dbf("C:/Niccolai/01_PhD/Papers/Paper003/GIS_LAYERS/CB_CRLOCS_ADJ_ALL_PR
EDINT99_Buffer.dbf")
head(crown.data)

## Visualize the newly created poly object.
plot(crown.poly, col="orange", main="")

crown.super.io <- list(crown.poly[1,])
looplen <- nrow(crown.data)
for ( i in 2:looplen){
i <- list(crown.poly[i,])
crown.super.io <- c(crown.super.io, i)
}

plot(crown.super.io[[1]], col="blue", add=TRUE)

Hope that helps!


Andrew Niccolai
Doctoral Candidate
Yale School of Forestry


 
-----Original Message-----
From: r-sig-geo-bounces at stat.math.ethz.ch
[mailto:r-sig-geo-bounces at stat.math.ethz.ch] On Behalf Of Agustin Lobo
Sent: Tuesday, April 08, 2008 9:02 AM
To: r-sig-geo at stat.math.ethz.ch
Subject: [R-sig-Geo] extracting polygons

Dear list,

I want to distribute a set of N circles according to a random distribution
within a set of polygons (N circles within each polygon).

I have an object of class SpatialPolygonsDataFrame with the polygons.

My idea is to use something like:

for (i in 1:length(absUTMpolys at polygons)){
  delme <- runifpoint(3, win=as.owin(absUTMpolys at polygons[i]))
  ...

but I'm not being successful at extracting each polygon and
as.owin refuses the conversion:

I've tried
 > as(absUTMpolys at polygons[1], "owin")
Error in as(absUTMpolys at polygons[1], "owin") :
   no method or default for coercing "list" to "owin"

and
 > as(absUTMpolys at polygons[1][[1]], "owin")
Error in as(absUTMpolys at polygons[1][[1]], "owin") :
   no method or default for coercing "Polygons" to "owin"


which is the proper way
of selecting each polygon from within the SpatialPolygonsDataFrame
object?

Thanks!

Agus


-- 
Dr. Agustin Lobo
Institut de Ciencies de la Terra "Jaume Almera" (CSIC)
LLuis Sole Sabaris s/n
08028 Barcelona
Spain
Tel. 34 934095410
Fax. 34 934110012
email: Agustin.Lobo at ija.csic.es
http://www.ija.csic.es/gt/obster

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