[R-sig-Geo] Looping over spatial data

[Roger Bivand]

On Thu, 10 Sep 2009, Jason Bryer wrote:

> Sorry for what may be a simple question. I am having an issue looping over 
> spatial data. Here is the code:
>
> usa.map = read.shape(file.choose()) #Shape file of the US, 51 records

There is a reason for read.shape() saying that it is deprecated. Please 
use classes defined in the sp package, and methods to read them, here 
possiblt readShapeSpatial() in maptools.

>
> pt = data.frame(x=-73.793, y=42.857)

If pt is a SpatialPoints object, you just use an overlay() method.

> shapes = Map2poly(usa.map)
> shape = shapes[[35]] #This is New York
>
> pip(pt, shape) #This works, returns the point as I expect since it is within 
> NY
>
> for(i in 1:length(shapes)) {
> 	shape = shapes[[i]]
> 	pip(pt, shape)
> 	#This is where the error occurs
> }
>
> This is the error I get:
>
> Error in inout(pt, shape) : NA/NaN/Inf in foreign function call (arg 4).
>

Almost certainly your assumption that the shape is a single ring is not 
met for some i, leading the splancs functions you are using to fail. Use 
sp classes, they are there to help.

Roger

> Thanks for any help.
>
> -Jason
>
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-- 
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