[R-sig-Geo] help tp select points of border with spatstat

[Rolf Turner]

On 11/02/2011, at 9:56 AM, gianni lavaredo wrote:

> Dear Researchers,
>
> I have a points shapefile with wave shape. I wish to select only  
> the border
> points to create a border owin with the same wave shape. I tryed to  
> use
> convex.hull but the final shape is not the same. Some researchers  
> have some
> suggestions?

If I understand your question correctly, what you should do is create
a data frame (say ``DF'') with columns "x" and "y" specifying the  
coordinates of
the points on (the border of) your ``wave shape''.  The points should  
be listed
in the ***anticlockwise*** direction, and the last point should  
***not*** repeat
the first.  Then do

	W <- owin(poly=DF)

HTH.

	cheers,

		Rolf Turner