[R-sig-Geo] spplot handling of overlapping points?

[Mauricio Zambrano-Bigiarini]

On 06/03/12 16:55, Edzer Pebesma wrote:
> Yes, look for argument alpha e.g. in ?rgb or ?bpy.colors

Thank you very much Edzer. It works perfectly:

library(sp)
xyz = data.frame(expand.grid(x=1:10,y=1:10),rnorm(100))
coordinates(xyz)=~x+y
spplot(xyz, cex=10, alpha=0.7)

Cheers,

Mauricio

-- 
=======================================================
FLOODS Action
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European Commission, Joint Research Centre (JRC)
webinfo    : http://floods.jrc.ec.europa.eu/
=======================================================
DISCLAIMER:
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and may not in any circumstances be regarded as stating
an official position of the European Commission."
=======================================================
Linux user #454569 -- Ubuntu user #17469
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"If Columbus had turned back, no one would have blamed him.
Of course, no one would have remembered him either."
(Source Unknown)
>
> On 03/06/2012 04:49 PM, Mauricio Zambrano-Bigiarini wrote:
>> On 05/03/12 14:40, Edzer Pebesma wrote:
>>> This has now been changed/repared in sp on r-forge (svn), and will
>>> appear from sp 0.9-97 on. A test run would be:
>>>
>>> library(sp)
>>> xyz = data.frame(expand.grid(x=1:10,y=1:10),rnorm(100))
>>> coordinates(xyz)=~x+y
>>> spplot(xyz, cex=10)
>>>
>>> which used to plot points in value order, and does now in data record
>>> order.
>>>
>>> I put up resulting graphs, for comparison, at
>>> http://ifgi.uni-muenster.de/~epebe_01/xyz.html
>>>
>>> As this change may make some of your spplot's for points different, if
>>> there are objections against this change (which I consider an
>>> improvement, if not a bug fix), it is time now to let me / us know.
>>
>> Would it be possible to set a degree of transparency  for the
>> overlapping points in spplot ?
>>
>> Thanks in advance,
>>
>> Mauricio Zambrano-Bigiarini
>> -
>> =======================================================
>> FLOODS Action
>> Water Resources Unit (H01)
>> Institute for Environment and Sustainability (IES)
>> European Commission, Joint Research Centre (JRC)
>> webinfo    : http://floods.jrc.ec.europa.eu/
>> =======================================================
>> DISCLAIMER:
>> "The views expressed are purely those of the writer
>> and may not in any circumstances be regarded as stating
>> an official position of the European Commission."
>> =======================================================
>> Linux user #454569 -- Ubuntu user #17469
>> =======================================================
>> "If Columbus had turned back, no one would have blamed him.
>> Of course, no one would have remembered him either."
>> (Source Unknown)
>>
>>
>>>
>>> On 03/02/2012 09:03 PM, MacQueen, Don wrote:
>>>> I have a SpatialPointsDataFrame object in which many points are very
>>>> close
>>>> together, such that the markers (plotting characters) tend to
>>>> overlap. (Of
>>>> course, this depends on marker size and the scale at which I plot; if I
>>>> "zoom in" there is less overlap.)
>>>>
>>>> It appears that when markers overlap, spplot() places a marker
>>>> associated
>>>> with the larger value after, and therefore on top of, a marker
>>>> associated
>>>> with a smaller value.
>>>>
>>>> Am I correct? Or more generally, what is the algorithm that
>>>> determines the
>>>> order in which markers are added?
>>>>
>>>>
>>>> I have searched ?spplot and related help pages and haven't found an
>>>> explanation (at least, not yet).
>>>>
>>>> I can add that I don't believe markers are placed in the order in which
>>>> they appear in the SpatialPointsDataFrame. I say this because when I
>>>> attempt to reproduce an spplot using base graphics plot() I have to sort
>>>> from smallest to largest value to succeed.
>>>>
>>>> I can probably provide a small reproducible example if necessary, but
>>>> I'm
>>>> hoping it's not necessary.
>>>>
>>>> Here are my actual commands.
>>>>
>>>>     tmps is the SpatialPointsDataFrame.
>>>>     tmp is coordinates(tmps)
>>>> (they have the same number of rows in the same order)
>>>>
>>>> Note that I'm using the cuts argument to break a continuous variable
>>>> ('cpm2') into bins. I have carefully matched the colors in tmps$col2
>>>> with
>>>> the cbin.cols object passed to spplot(), and the break points for the
>>>> bin
>>>> boundaries, so I believe that everything else that could affect the
>>>> final
>>>> appearance, other than the order in which the markers are placed, is
>>>> controlled.
>>>>
>>>> #1 using spplot
>>>> spplot(tmps,c('cpm2'),
>>>>      key.space='right',
>>>>      legendEntries=cbin.lbls,
>>>>      cuts=cbin.brks,
>>>>      col.regions=cbin.cols,
>>>>      cex=0.4)
>>>>
>>>> #2 using base graphics
>>>> plot(tmp[,1],tmp[,2], asp=1, cex=0.6, pch=16, col=tmps$col2)
>>>>
>>>>
>>>>
>>>> Thanks
>>>> -Don
>>>>
>>>
>>
>>
>> -
>