Question:manipulating spatial data using combination of Maptools and Splancs

Hi,
I have a problem that concerns combination of the package Maptools and 
Splancs
I have 2 shapefiles that i want to manipulate (one of type point and one 
polygon).I import them in R using Maptools but then i can't estimate a 
quartic Kernel using Splancs. The package doesn't recognize the shapes 
(invalid points and poly argument).I don't know if this is an easy task but 
i have read both packages's manual and i can't find a liable solution. Thank 
u for your time.

Say you have a shapefile of points, and a shapefile with one single ring 
polygon, no holes or other geometry objects, then using maptools 0.5-2:

library(maptools)

Loading required package: foreign
Loading required package: sp

cardiff_pts <- readShapePoints("cf_pts")
cardiff_poly <- readShapePoly("cf_poly", verbose=TRUE)

Shapefile type: Polygon, (5), # of Shapes: 1

plot(cardiff_poly)
plot(cardiff_pts, add=TRUE)

Conversion is by

splancs_pts <- coordinates(cardiff_pts)
splancs_poly <- getPolygonCoordsSlot(getPolygonsPolygonsSlot(

+    getSpPpolygonsSlot(cardiff_poly)[[1]])[[1]])

to unpack the coordinates of the points and the single ring boundary. If 
you have more than one shape, and/or more than one ring in that shape, 
adjust the [[Shape]])[[ring]] indices to suit. Then:

polymap(splancs_poly)
image(kernel2d(splancs_pts, splancs_poly, h0=15, nx=100, ny=100), 

+    add=TRUE)

pointmap(splancs_pts, add=TRUE)

works as expected. Extracting the polygon looks complicated because 
shapefiles have a "richer" geometry than splancs. Wrapper functions for 
splancs to use the sp classes now used by maptools will be available 
before long.

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Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
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Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no

Thank you for your advice but i still have a problem...Everything goes fine 
till the plotting (as usual).When i try the code you posted for the 
conversion i get the following message:

Error in coordinates(quakes) : no direct or inherited method for function 
'coordinates' for this call

i don't have a clue what this means...

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Thank you for your advice but i still have a problem...Everything goes fine 
till the plotting (as usual).When i try the code you posted for the 
conversion i get the following message:

Error in coordinates(quakes) : no direct or inherited method for function 
'coordinates' for this call

i don't have a clue what this means...

Please always include the commands you gave, here in particular the
command(s) creating the quakes object - other list participants cannot see
your computer screen. All the error message says is that it is not a
SpatialPoints* object, so you have not done:

quakes <- readShapePoints("quakes.shp")
quakes_pts <- coordinates(quakes)

as I suggested. I also suggest moving this thread to the R-sig-geo list - 
subscription details on the "Spatial" Task View on CRAN:

http://cran.r-project.org/src/contrib/Views/Spatial.html

Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no