plot polygons - transparent holes/island

On Mon, 1 Feb 2010, Paulo Eduardo Cardoso wrote:

Hi,
Code exemple
library(maptools)
load(file='D:\\R\\transparencia\\TransparentPolygon.Rdata')
areas <- readShapeSpatial('D:\\R\\transparencia\\Areas.shp')
pontos <- readShapeSpatial('D:\\R\\transparencia\\Points.shp')
plot(pontos,pch=19,col=pontos$point)
plot(areas,pbg="transparent",bg="red",add=TRUE)

data can be downloaded from

http://rapidshare.com/files/344532718/TransparentPolygon.Rdata.html

example image can be downloaded grom

http://rapidshare.com/files/344533300/ExampleTransparentPolygon.png.html

The image cannot be reproduced with your plotting order, because the
polygons overpaint the points. Crucially, the big square is completely
painted. You also have two Polygons objects, one a square with a round hole,
the other an island filling the hole. With your objects, you could do:

plot(areas[1,], pbg="white", col="grey85", border="grey50") # set up
background polygon and paint hole
plot(areas[2,], angle=45, density=8, border="grey50", col="grey50",
?add=TRUE)
# hatch the island polygon
points(pontos[pontos$point=="in",], pch=16)
# add the in points
points(pontos[pontos$point=="out",], pch=22, col="grey50", bg="grey50")
# and the out points

If your output devive uses and alpha channel, you may be able to find other
ways forward, but they will not be portable across devices.

Hope this helps,

Roger

2010/1/31 Roger Bivand <Roger.Bivand at nhh.no>

On Sun, 31 Jan 2010, Paulo Eduardo Cardoso wrote:

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?

Please do, either code for a provided data set, or code and a link to the
URL where the data set is available.

Roger

2010/1/30 Roger Bivand <Roger.Bivand at 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

? ? ? [[alternative HTML version deleted]]

--
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

--
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

--
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