[R-sig-Geo] (no subject)

[Roger Bivand]

On Thu, 15 Mar 2007, Adrian Baddeley wrote:

> 
> On Tue, 13 Mar 2007, Michael Friendly wrote:
> 
> > I've read the documentation, but can't find an example of how 
> > to specify a circular window for the ppp object that would contain the
> > data and the window.
> 
> To create a circular window in spatstat, you can use the 
> function disc(). See help(disc). 
> 
> For example suppose a point pattern with coordinates x, y (two vectors)
> is observed inside a pot with centre (x0, y0) and radius R.
> Then 
> 	   pot <- disc(R, c(x0,y0))
> creates a window (owin object) representing the pot,
> and
> 	   X <- ppp(x, y, window=pot)
> creates the point pattern. 
> 
> Since spatstat always plots spatial objects isometrically, you can also 
> use plot(disc(....)) just to draw a circle. 
> 
> > The data structure is something like a data frame for all the 
> > germinating seeds, recording (X,Y) location and maybe some other
> > measure like size after xx days:
> > 
> > PotID Treatment SeedType  X    Y  size
> 
> Currently, a point pattern can only have one mark variable
> (e.g. you can attach the SeedType to each point, or attach the size to
> each point, but not both).
> This will change in spatstat version 2 which will be released soon.
> 
> > (Is there something better?) 
> 
> There is nothing better than spatstat!  %^]

Great!

To get to the sp Polygon object:

res0 <- disc(1, c(0,0))$bdry
res <- Polygon(rbind(res0, res0[1,]))

should anyone need it.

Roger


> 
> regards
> Adrian Baddeley
> 

-- 
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