[R-sig-Geo] interoperating SpatialLinesDataFrame, SpatialPolygonsDataFrame

[Edzer Pebesma]

Tom, say x is your SpatialPolygonsDataFrame, did you try the obvious,

as(x, "SpatialLinesDataFrame")

?

On 02/25/2013 11:18 PM, Tom Roche wrote:
>
> How to cast SpatialPolygonsDataFrame (SPDF) to SpatialLinesDataFrame
> (SLDF), or vice versa? Alternatively, how best to write a function to
> use either an SPDF or an SLDF as a map overlay in levelplot(...)?
> Why I ask:
>
> https://bitbucket.org/tlroche/clm_cn_global_to_aqmeii-na
>
> regrids a dataset from global/unprojected to LCC over a superset of
> CONUS ("AQMEII-NA"). I currently have code that gets a projected map
> of the CONUS state boundaries with
>
> + state.map <- maps::map(
> +   database="state", projection="lambert", par=c(33,45), plot=FALSE)
>
> tweaks the coordinates, and converts the map to an SLDF
>
>> state.map.IOAPI.shp <-
>>    maptools::map2SpatialLines(state.map.IOAPI, proj4string=out.crs)
>
> I then pass the SLDF to a function (which I wrote because I'll be
> repeating this task with different datasets) to overlay that map onto
> plots of the layers of a RasterBrick:
>
>> plot(rasterVis::levelplot(brick,
>>    margin=FALSE,
>>    layout=c(1,length(names(brick)))
>> ) +
>>    latticeExtra::layer(
>>      sp::sp.lines(map.shp, lwd=0.8, col='darkgray')))
>
> I want to include Canada and Mexico in my map overlay, since the
> horizontal domain includes large portions. I can do
>
>> library(maptools)
>> data(wrld_simpl) # from maptools
>> map.noram.shp.unproj <-
>>    wrld_simpl[wrld_simpl$ISO3 %in% c('CAN', 'MEX', 'USA'),]
>> map.noram.shp.proj <-
>>    rgdal::spTransform(map.noram.shp.unproj, CRS=out.crs)
>
> But the latter is an SPDF, for which my function above throws an error
> (since sp::sp.lines wants a SLDF). I'm guessing I could change the code
> to use sp::sp.polygons as needed (with some sort of `if` or `case`
> checking the class of the map), but I'd much prefer to just convert the
> SPDF to an SLDF (since I'm not using the polygon's fill or other
> attributes). How best to do that? Or is the way to do this Something
> Completely Different?
>
> Apologies if this is a FAQ, but I'm not seeing the answer in doc
> (sp.pdf or intro_sp.pdf) or via googling.
>
> TIA, Tom Roche <Tom_Roche at pobox.com>
>
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>

-- 
Edzer Pebesma
Institute for Geoinformatics (ifgi), University of Münster
Weseler Straße 253, 48151 Münster, Germany. Phone: +49 251
8333081, Fax: +49 251 8339763  http://ifgi.uni-muenster.de
http://www.52north.org/geostatistics      e.pebesma at wwu.de