distmap

I've tried (among other things):
 > limit1 <- read.shape("limit_PNSN2000.shp")
Shapefile type: Polygon, (5), # of Shapes: 2
 > limit1poly <- Map2poly(limit1)
 > limit1owin <- as(limit1poly,"owin")
Error in .classEnv(thisClass) : unable to find an environment containing 
class "polylist"

 > limit2 <- readOGR("limit_PNSN2000.shp",layer="limit_PNSN2000")
OGR data source with driver: ESRI Shapefile
Source: "limit_PNSN2000.shp", layer: "limit_PNSN2000"
with  2  rows and  1  columns
 > limit2poly <- Map2poly(limit1)
 > limit1owin <- as(limit2poly,"owin")
Error in .classEnv(thisClass) : unable to find an environment containing 
class "polylist"
 > limit1owin <- as(limit2,"owin")
Error in as.owin.SpatialPolygons(from) : W must be a SpatialPolygons object

I guess all I need is to convert my shapefile (read into R via 
read.shape or readOGR?) into an object like letterR:

 > data(letterR)
 > str(letterR)
List of 4
  $ type  : chr "polygonal"
  $ xrange: num [1:2] 2.02 3.93
  $ yrange: num [1:2] 0.645 3.278
  $ bdry  :List of 2
   ..$ :List of 2
   .. ..$ x: num [1:24] 2.03 2.02 2.02 2.66 2.66 ...
   .. ..$ y: num [1:24] 3.278 3.248 0.653 0.653 1.695 ...
   ..$ :List of 2
   .. ..$ x: num [1:10] 2.65 2.64 3.04 3.12 3.16 ...
   .. ..$ y: num [1:10] 2.23 2.70 2.71 2.63 2.50 ...
  - attr(*, "class")= chr "owin"

but how can I do it?

Also, I'm so confused with so many spatial objects, is there a guide?

Agus

Roger Bivand escribi?:

On Fri, 22 Jun 2007, Agustin Lobo wrote:

Dear sig-geos,

I have to calculate a distmap (that is, a map
in which the value of each cell is the distance
from the cell to a given object) for a set of polygons.
It seems to me that distmap.owin in spatstat would do it
fine, but distmap.owin does not accept objects
imported from shp vectors via readOGR. distmap.owin requires
type "polygonal" and readOGR yields class 'SpatialPolygonsDataFrame'
Is there any way to cast or convert from 'SpatialPolygonsDataFrame'
to "polygonal" or an alternative function to calculate the distances
to the boundaries of the polygons?

Have you tried coercing with as(x, "owin") in maptools?

Roger

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