[R-sig-Geo] plot polygons - transparent holes/island

[Paulo Eduardo Cardoso]

Hi,

A good work around for representation but not exactly what was
expected for the real dataset.

The image with alpha channel (transparency) is just a schema to
provide the idea of hidden points but they are not supposed to be
visible. Sorry.

Considering that all points are plotted at first, wihout using
"in-out", is there a way to overlap areas[1,] keeping "in" points
visible?

Paulo


2010/2/2 Roger Bivand <Roger.Bivand at nhh.no>:
> 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]]
>>>>>>
>>>>>> _______________________________________________
>>>>>> R-sig-Geo mailing list
>>>>>> R-sig-Geo at stat.math.ethz.ch
>>>>>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>>>>>>
>>>>>>
>>>>> --
>>>>> 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
>