[R-sig-Geo] background colour when add=T

[Rob Robinson]

Thanks Greg & Matthew. I have multiple polygons (a world map from the
wonderful naturalearthdata.com), so gDifference does exactly what I
needed. If the developers of rgeos are listening - thanks to them for
a seriously awesome package!
best wishes
rob

**************  Find out about Britain's birds - www.bto.org/birdfacts
 **************

Dr Rob Robinson, Principal Ecologist
British Trust for Ornithology, The Nunnery, Thetford, Norfolk, IP24 2PU
Ph: +44 (0)1842 750050     E: rob.robinson at bto.org
Fx: +44 (0)1842 750030     W: www.bto.org/about-bto/our-staff/rob-robinson

====== "How can anyone be enlightened, when truth is so poorly lit" =======



On 13 September 2012 18:58, Matthew Landis <landis at isciences.com> wrote:
> Rob -
> Without seeing your code, I'm not exactly sure what you are trying to do.
> But, I routinely control the appearance of land vs. sea with a setup
> something like this:
>
> bg.spdf    # a spatialPolygonsDataFrame with 1 polygon for ocean and 1 for
> land
> bg.fill  <- c('transparent', 'gray')   # If the wrong one is filled, switch
> order
> data.sgdf   # A spatialGridDataFrame of the data I want to plot
>
> spplot(data.sgdf, panel = function(x, y, ...){
>         sp.polygons(bg.spdf, fill = bg.fill)
>         })
>
> Hope that helps.
>
> M
>
>
> On 9/13/2012 1:29 PM, Greg Snow wrote:
>>
>> One possibility would be to define a spatial polygon that represents
>> the entire plotting area, then use the gDifference function from the
>> rgeos package to create a map that excludes the land areas (or
>> whatever you don't want to cover) and add the resulting polygon(s).
>>
>> On Thu, Sep 13, 2012 at 8:04 AM, Rob Robinson <rob.robinson at bto.org>
>> wrote:
>>>
>>> Dear All,
>>>   I am trying to plot some abundance density maps for different species
>>> of birds which may be either marine or terrestrial. Having created the
>>> density kernel (using kde from package ks), I plot() a background map
>>> (actually a SpatialPolygonsDataFrame) and I can colour the land and
>>> sea differently using col= and bg= options respectively, I can then
>>> overlay my kernel using filled.contour. What I would now like to do is
>>> mask the inappropriate part of the map. For marine birds this is easy,
>>> simply replot the map using add=T and col= to 'blank' out the part of
>>> the kernel over land. I thought the same would be true for landbirds,
>>> simply use bg= to mask out the sea. Unfortunately when you have add=T
>>> plot (not unreasonably, I suppose) doesn't seem to honour the bg=
>>> argument, it just (I presume) sets it to 'transparent'. Does anyone
>>> know if there is a way to subvert this? A posting from a couple of
>>> years ago suggests probably not, but I wondered if anything had
>>> changed in the interim?
>>> many thanks in advance for any insights...
>>> cheers
>>> rob
>>>
>>> **************  Find out about Britain's birds - www.bto.org/birdfacts
>>>   **************
>>>
>>> Dr Rob Robinson, Principal Ecologist
>>> British Trust for Ornithology, The Nunnery, Thetford, Norfolk, IP24 2PU
>>> Ph: +44 (0)1842 750050     E: rob.robinson at bto.org
>>> Fx: +44 (0)1842 750030     W:
>>> www.bto.org/about-bto/our-staff/rob-robinson
>>>
>>> ====== "How can anyone be enlightened, when truth is so poorly lit"
>>> =======
>>>
>>> _______________________________________________
>>> R-sig-Geo mailing list
>>> R-sig-Geo at r-project.org
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>>
>>
>>
>
> --
> ~~~~~~~~~~~~~~~~~~~~~~~~~~
> Matthew Landis, Ph.D.
> Research Scientist
> ISciences, LLC
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> ~~~~~~~~~~~~~~~~~~~~~~~~~~
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