[R-sig-Geo] raster::plot() common color scale?

[Agustin Lobo]

Paul,

While this is certainly the most elegant solution, would it work with
really large raster objects? Note that you
make a data.frame, and the most important characteristic of package
raster is its ability to do not incorporate
the actual raster values to the raster objects to save memory.

Would this problem be avoided by the new wrapper provided by Robert?

Thanks

Agus

2011/6/10 Paul Hiemstra <paul.hiemstra at knmi.nl>:
>  Hi,
>
> I would recommend using one of the more advanced plotting facilities in
> R, ggplot. An example:
>
> library(ggplot2)
> library(raster)
> theme_set(theme_bw())
>
> r = raster(system.file("external/test.grd", package="raster"))
>
> # Convert to data.frame
> r_df = as.data.frame(as(r, 'SpatialPixelsDataFrame'))
> # create new column 10 times larger
> # here you could extract data from other grids that
> # you want to show at the same time
> r_df$valuesx10 = r_df$values*2
>
> # Reshape the data for ggplot
> plotData = melt(r_df, id.vars = c('x','y'))
>
> ggplot(aes(x = x, y = y), data = plotData) +
>    geom_tile(aes(fill = value)) + facet_wrap(~ variable) +
>    scale_fill_gradient(low = 'white', high = 'blue') +
>    coord_equal()
>
> This is a basic ggplot example of visualizing rasters. I realize that it
> is a short example with a lot of things specific to ggplot, but I hope
> you can figure out why I use the code that I use. In my view, the
> investment in learning to use ggplot is worth it. A good place to start
> is the ggplot website [1].
>
> cheers.
> Paul
>
> [1] http://had.co.nz/ggplot2/
>
> On 06/09/2011 01:59 PM, Agustin Lobo wrote:
>> Hi!
>> I'm doing
>>
>> par(mfrow=c(2,2))
>> plot(simr)
>> plot(simrlisa)
>> a2 = simr>l$lisamax
>> plot(l$lisamax)
>> plot(simr*a2)
>>
>> where simr, l%lisamax and a2 are raster objects. Is there any way to
>> get a common color scheme
>> (i.e., setting common min and max values)?
>> The color table is the same, but the scaling is independent for each
>> raster object and cannot be compared.
>>
>> Thanks
>>
>> Agus
>>
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>
>
> --
> Paul Hiemstra, Ph.D.
> Global Climate Division
> Royal Netherlands Meteorological Institute (KNMI)
> Wilhelminalaan 10 | 3732 GK | De Bilt | Kamer B 3.39
> P.O. Box 201 | 3730 AE | De Bilt
> tel: +31 30 2206 494
>
> http://intamap.geo.uu.nl/~paul
> http://nl.linkedin.com/pub/paul-hiemstra/20/30b/770
>
>