kriging inside borders

On Fri, 20 May 2005, Chloe ARCHINARD wrote:

My exact commands are :
library(maptools)
shapefile=read.shape('my.shp')
x=Map2poly(shapefile)

and the length is :
length(mappolys)
[1] 615

OK. So what I think you have is a grid of cells, possibly with cells 
missing around the edges and maybe in the middle too. The splancs polygon 
cannot have holes, by the way. I think that what you could do is to choose 
the locations= values you need within the polygon grid first, and not use 
borders=. I've tried to replicate your situation, and have made a 
shapefile with rectangular grid cells with uneven edges and a hole. Then I 
did:

library(sp)
library(maptools)
shapefile <- read.shape("<your file>.shp")
x <- as.SpatialRings.Shapes(shapefile$Shapes, IDs=1:length(shapefile$Shapes))
xp <- SpatialPoints(cbind(runif(50, 0, 3), runif(50, 0, 3)))

# here you do xp <- SpatialPoints(<your location points matrix>)

res <- overlay(x, xp)

# overlay() sets the value of res to the ID of the polygon the point falls 
# in, or to NA if the point does not fall in any polygon.

plot(x, col="grey")
points(xp[is.na(res)], col="red")
points(xp[!is.na(res)], col="blue")

and you can choose the points for the prediction locations as:

<my prediction locations> <- xp[!is.na(res)]

xx <- xp[!is.na(res)]
class(xx)

class(coordinates(xx))

check.locations(xx)

check.locations(coordinates(xx))

Please check on the plot to see if overlay divides up the points correctly 
first, just to be sure. If this works, it is will be a nice example of how 
the coordination of spatial data functions in the "sp" package can make 
things easier (if not, any reports on difficulties with "sp" are always 
welcome).

Roger

 But i'm not sure that it's the good polylist object i need because it's
a polygon grid in fact.

Thank you for your help
Chlo?
-----Message d'origine-----
De?: Roger Bivand [mailto:Roger.Bivand at nhh.no] 
Envoy??: jeudi 19 mai 2005 19:07
??: Chloe ARCHINARD
Cc?: r-sig-geo at stat.math.ethz.ch
Objet?: Re: [R-sig-Geo] kriging inside borders

On Thu, 19 May 2005, Chloe ARCHINARD wrote:

Hello, I'm using geoR package to compute kriging with the function

krige.conv() and I used maptools (read.shape () + Map2poly () )  and

splancs (borders) packages to include a object of class polylist for the

attribute borders.

 But I've got this message of error when 'borders' is in krige.conv () :  

krige.conv: there are no prediction locations inside the borders.  My

polylist is not good? The coordinates seam to be OK when I draw a map

with this polylist object. And if I use 'borders' in the contour

function : message error is :

Error in as.data.frame.default(borders) : can't coerce class "polylist"

into a data.frame

Firstly, it does help if the exact commands are given, rather than your 

choice of them. I think the main issue here is that a polylist object is a 

list of matrices with attributes, not a matrix. If your polylist object 

is:


x <- Map2poly(read.shape("my.shp"))


what is length(x)? If it is 1, you may be able to say x[[1]] to extract 

the first matrix in the list, but even then it may not work. If you can 

show us the commands you are giving, and the length of your polylist 

object, it should be possible to find something that works. 

If someone could help me, thanks a lot!

Chlo? Archinard

-- 

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



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