[R-sig-Geo] fix color scale

[Edzer Pebesma]

Dylan, I believe that lattice (grid) recently improved the plotting of
rasters quite a bit, by using panel.levelplot.raster instead of
panel.levelplot - some function in grid now renders rasters faster on
devices for which this is optimed.

spplot also has to transform the data to long format, by calling
sp:::spmap.to.lev, which in turn uses a stack method for
SpatialPointsDataFrame objects; this in turn uses stack.data.frame

Bests,


On 11/08/2010 05:00 AM, Dylan Beaudette wrote:
> Interesting demonstration. However, it seems like sp objects and
> spplot are still more efficient at storing / plotting large grids. The
> example listed below required over 2 minutes to complete on a 2.4 Ghz
> Intel processor. Also, storing the coordinates + data in long format
> could easily fill available memory with large rasters. I have found
> that storing multiple raster attributes as columns in the @data slot
> of a SpatialGridDataFrame object give me flexibility to plot images
> with a consistent color scheme, without needing to store the data in
> long format. Also with lattice, the plots are generated in a couple of
> seconds (500x700 px grid). I would be very interested in knowing how
> to make ggplot() any faster.
> 
> Cheers!
> Dylan
> 
> On Sun, Nov 7, 2010 at 11:55 AM, Edzer Pebesma
> <edzer.pebesma at uni-muenster.de> wrote:
>> Paul, this nicely illustrates the power of ggplot2.
>>
>> In the resulting plot, however, it seems to me that the
>>
>> + opts(aspect.ratio = 1)
>>
>> does not result in the desired effect that 1 m in the x direction equals
>> 1 m in the y direction. Standard plot (asp = 1), and lattice plots (asp
>> = "iso") have this; what does ggplot2 need?
>>
>> On 10/31/2010 11:31 AM, Paul Hiemstra wrote:
>>> Hi Peter,
>>>
>>> When creating such a large amount of illustrations with the same
>>> colorscale, I automatically think of lattice graphics. Under the hood
>>> spplot also uses lattice graphics. Take a look at the levelplot()
>>> function from lattice which produces the grid plots for spplot (if I'm
>>> correct). Alternatively, I've been using ggplot now for quite a while to
>>> make plots of a lot of grids. A small example says more than a thousand
>>> words:
>>>
>>> library(ggplot2)
>>> library(sp)
>>>
>>> data(meuse.grid)
>>> summary(meuse.grid)
>>>
>>> # Note that I do not transform meuse.grid to SpatialPixelsDataFrame
>>> # Let's make a simple grid plot
>>> dum = meuse.grid[c("x","y","dist")]
>>> ggplot(aes(x = x, y = y, fill = dist), data = dum) + geom_tile()
>>>
>>> # Let's make a few more attributes to the grid
>>> # could be measurements on other dates for example
>>> new_atts = do.call("cbind", lapply(1:100, function(num) dum$dist +
>>> runif(dum$dist)))
>>> summary(new_atts)
>>> dum = data.frame(cbind(dum, new_atts))
>>>
>>> # Important step now is to
>>> # restructure the data
>>> dum_ggplot = melt(dum, id.vars = c("x","y"))
>>>
>>> # Now make a plot using dum_ggplot
>>> # of 'x' and 'y' using value as a 'fill'
>>> # with a plot per 'variable', can take a minute to plot
>>> ggplot(aes(x = x, y = y, fill = value), data = dum_ggplot) + geom_tile()
>>> + facet_wrap(~variable) +
>>>       scale_x_continuous('', labels = NA, breaks = NA) +
>>>       scale_y_continuous('', labels = NA, breaks = NA) +
>>> opts(aspect.ratio = 1)
>>> # These last two lines get rid of the labels on the axes and set aspect
>>> ratio to 1
>>>
>>> Now you have a plot with 101 maps with the same colorscale, with ggplot
>>> doing all the hard work. It takes some time to get the hang of ggplot,
>>> but I think it is worth the investment, also for spatial plots.
>>>
>>> cheers and hope this helps,
>>> Paul
>>>
>>> On 10/28/2010 09:12 PM, Peter Larson wrote:
>>>> Hello!
>>>>
>>>> I have a problem.
>>>>
>>>> I am using IDW to interpolate a daily series of geospatial
>>>> observations. Thus, I want to produce a large number of sequential
>>>> maps.
>>>>
>>>> I want them to all represent the same color scale. Is there any way to
>>>> fix the color scale so that it is the same for all the plots?
>>>>
>>>> Thanks,
>>>>
>>>> Pete
>>>>
>>>> _______________________________________________
>>>> R-sig-Geo mailing list
>>>> R-sig-Geo at stat.math.ethz.ch
>>>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>>>>
>>>
>>>
>>
>> --
>> 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
>>
>> _______________________________________________
>> R-sig-Geo mailing list
>> R-sig-Geo at stat.math.ethz.ch
>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>>

-- 
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