[R] Filling polygons with points

[Roger Bivand]

On Thu, 14 Oct 2004, Petr Pikal wrote:

> 
> 
> On 14 Oct 2004 at 10:00, Duncan Murdoch wrote:
> 
> > On Thu, 14 Oct 2004 15:16:30 +0200, "Wolf, Michael"
> > <Michael.Wolf at bezreg-muenster.nrw.de> wrote :
> > 
> > >Dear list,
> > >
> > >are there any possibilities to fill a polygon with a point pattern or
> > >with a symbol pattern like '+' oder '-' instead of shading lines?
> > 
> > I don't think the graphics devices know how to do that, but you could
> > program it yourself:
> > 
> > Supposed interior(x,y) is a function that determines whether the
> > points (x,y) are in the polygon, then just create a grid of locations,
> > subset when interior(x,y) is true, and plot using pch='+'.
> > 
> > I made a quick search and was unable to find a general implementation
> > of the "interior" function for an arbitrary polygon; I'm a bit
> > surprised about that.  Hopefully someone else can point to one,
> 
> Hi
> 
> I think that you can find such functionity in splancs package 
> probably function pip() find if points are inside or outside of the 
> polygon.
> 
> Cheers
> Petr
> 

Going a bit further, you could use areapl() and gridpts() in splancs to 
return plotting points for the symbols that would give an even symbol per 
unit area coverage. This is a very similar question to:

https://stat.ethz.ch/pipermail/r-help/2004-September/056351.html

which was about dot density maps. A function to do that will be in the 
next maptools, but I think this is a bit different and is more like a 
hatching but with arbitrary symbols and chosen spacing - it can be done, 
but do you need this kind of symbology?

Roger

> 
> 
> > otherwise please write one, and document it and contribute it to R.
> > It's a relatively standard algorithm, and would be useful.
> > 
> > Duncan Murdoch
> > 
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> 
> Petr Pikal
> petr.pikal at precheza.cz
> 
> ______________________________________________
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-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Breiviksveien 40, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 93 93
e-mail: Roger.Bivand at nhh.no