Roger,

I really thank you for you comments. You are always available to explain
everything, and that's a fortune for forum users.
But I still with the same problem. I did,'t understand how to leave the
inner hole or the inner polygon transparent, in order to see any other layer
plotter at first.
Should I send a simple example?

2010/1/30 Roger Bivand <Roger.Bivand@nhh.no>

> On Sat, 30 Jan 2010, Paulo Eduardo Cardoso wrote:
>
>  I'd like to plot a SPDF with two objects, one of them buffering the other
>> "island". How can I set the "island" transparent?
>> Similarly, keeping the outer polygon only, how can the hole still
>> transparent?
>>
>
> Polygons objects are plotted largest to smallest, as are Polygon objects in
> each Polygons object. Each Polygons object and all its constituent Polygon
> objects are painted the colour chosen for that Polygons object.
>
> If you want the holes Polygon objects to overpaint their containing Polygon
> objects, in the base graphics plot() method, you set the pbg= argument to
> the background colour (not "transparent", this will let you see the painted
> Polygon below). In the spplot method, this is handled internally by reading
> the trellis.par.get()$background value, and using it if not "transparent",
> or "white" if it is "transparent".
>
> Both approaches depend on the hole slot of the Polygon object being
> correctly set.
>
> R graphics do not analyse objects leaving out say holes, they overpaint.
> This is because the holes are not "known" in advance by the functions being
> executed.
>
> Hope this helps,
>
> Roger
>
>
>> Thanks in advance,
>>
>> Paulo E. Cardoso
>>
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>>
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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@nhh.no
>
>

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