[R-sig-Geo] suggestion for sp.grid()

[Edzer Pebesma]

Thanks for the clear example, Dylan. I made this change, and it will be
in the next version of sp.

On 12/15/2010 05:57 PM, Dylan Beaudette wrote:
> Shouldn't be posting questions late into the night. I realized that my
> example was not reproducible.
> 
> One more time:
> 
> # setup environment
> library(gstat)
> library(latticeExtra)
> library(grid)
> 
> # load example data
> data(meuse.grid)
> 
> coordinates(meuse.grid) <- ~ x + y
> gridded(meuse.grid) <- TRUE
> meuse.grid$soil <- factor(meuse.grid$soil, labels=c('A','B','C'))
> 
> 
> # hacked version of sp.grid()
> sp.grid <- function (obj, col = 1, alpha = 1, ...)
> {
>     if (is.character(obj))
>         obj = get(obj)
>     xy = coordinates(obj)
>     if (length(col) != 1 && length(col) != nrow(xy)) {
>     }
>     gt = as(getGridTopology(obj), "data.frame")
>     grid.rect(x = xy[, 1], y = xy[, 2], width = gt$cellsize[1],
>         height = gt$cellsize[2], default.units = "native", gp =
> gpar(fill = col, col = NA, alpha = alpha))
> }
> 
> 
> trellis.par.set(regions=custom.theme()$regions,
> superpose.polygon=list(col='black', alpha=0.25))
> 
> # first grid covers entire extent
> p3 <- spplot(meuse.grid, 'dist', colorkey=list(space='bottom',
> width=1, height=0.5, tick.number=3))
> 
> # overlay partially transparent, kind of a hack...
> p3 <- p3 + layer(sp.grid(meuse.grid[meuse.grid$soil == 'A', ],
> col='black', alpha=0.25))
> 
> p3 <- update(p3, key=simpleKey('Shaded Region', points=FALSE,
> lines=FALSE, rect=TRUE, columns=1, space='top'))
> 
> p3
> 
> 
> 
> 
> On Tue, Dec 14, 2010 at 11:32 PM, Dylan Beaudette
> <dylan.beaudette at gmail.com> wrote:
>> Hi,
>>
>> I was tinkering around with some of the new functions from the
>> latticeExtra package, and thought of a (messy) hack for plotting
>> multiple grids. However, due to the way sp.grid() is currently coded,
>> there is no way to define both grid fill color _and_ outline color:
>>
>> gp = gpar(fill = col, col = NULL, alpha = alpha)
>>
>> if this line is changed to...
>>
>> gp = gpar(fill = col, col = NA, alpha = alpha)
>>
>> then outlines will default to no color... It might be nice to add a
>> new parameter to sp.grid() to allow the user to set the outline color
>> of the rectangles produced by grid.rect(). If the above line is
>> changed so that col=NA, then it is possible to overlay two grids (kind
>> of) like this:
>>
>>
>> library(gstat)
>> library(latticeExtra)
>> library(grid)
>>
>> # load example data
>> data(meuse.grid)
>> coordinates(meuse.grid) <- ~ x + y
>> gridded(meuse.grid) <- TRUE
>>
>> # hacked version of sp.grid()
>> sp.grid <- function (obj, col = 1, alpha = 1, ...)
>> {
>>    if (is.character(obj))
>>        obj = get(obj)
>>    xy = coordinates(obj)
>>    if (length(col) != 1 && length(col) != nrow(xy)) {
>>    }
>>    gt = as(getGridTopology(obj), "data.frame")
>>    grid.rect(x = xy[, 1], y = xy[, 2], width = gt$cellsize[1],
>>        height = gt$cellsize[2], default.units = "native", gp =
>> gpar(fill = col, col = NA, alpha = alpha))
>> }
>>
>>
>> # nice colors
>> trellis.par.set(regions=custom.theme()$regions,
>> superpose.polygon=list(col='black', alpha=0.25))
>>
>> # first grid covers entire extent
>> p3 <- spplot(meuse.grid, 'dist', colorkey=list(space='bottom',
>> width=1, height=0.5, tick.number=3)
>>
>> # overlay partially transparent, kind of a hack...
>> p3 <- p3 + layer(sp.grid(meuse.grid[meuse.grid$soil == 'A', ],
>> col='black', alpha=0.25))
>>
>> # add a new key
>> p3 <- update(p3, key=simpleKey('Bad Stuff', points=FALSE, lines=FALSE,
>> rect=TRUE, columns=1, space='top'))
>>
>> print(p3)
>>
>> Note that I am using an older version of gstat, version 0.9-63. Maybe
>> this code has been updated since then. If not, what do you think? Are
>> there any better ways to overlay a couple grids?
>>
>> Cheers,
>> Dylan
>>
> 
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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