[R] Filling polygons with points

[Adrian Baddeley]

<Michael.Wolf at bezreg-muenster.nrw.de> wrote :

 >Are there any possibilities to fill a polygon with a point pattern or
 >with a symbol pattern like '+' oder '-' instead of shading lines?

In `spatstat' there is code for testing whether points belong to
a spatial region. The region can consist of any number of polygons,
and the polygons may have holes, etc.

While splancs has similar functionality, spatstat additionally allows regions
defined by a binary image (e.g. a digital approximation to a circle). 

The code is available both as a function inside.owin(x,y,win)
and as a method for "[" for point pattern objects.

Example of "[":

	library(spatstat)
	data(demopat)
	w <- demopat$window               # an irregular polygonal window
	plot(w)

	g <- as.mask(w, dimyx=c(20,20))   # make a 20 x 20 grid
				            # enclosing the window

        g <- as.mask(w, eps = 200)       # or set absolute grid spacing 200

        p <- ppp(raster.x(g), raster.y(g), window=w)
                                            # convert to point pattern object
        p <- p[, w]   # clip points to window 

	plot(p)
	plot(p, pch="+")   # etc
	

To create a window object use owin() or as.owin().

Adrian Baddeley