[R-sig-Geo] Problems with plotting large factor-type rasters using the raster package

[Pascal Oettli]

Hello,

You can set a larger number of pixels in the "image" function:

> image(r2, maxpixels=5e6)

Or I missunderstood the problem.

Regards,
Pascal

On 23 January 2014 18:56, Tomislav Hengl <hengl at spatial-analyst.net> wrote:
>
> Hi Robert,
>
> I am having problems with plotting factor-type rasters using the raster
> package (v. 2.1-49). Here is the error message I get:
>
> library(raster)
> library(plotKML)
> ## smaller raster:
> data(eberg_grid)
> gridded(eberg_grid) <- ~x+y
> eberg_grid$CL <- cut(eberg_grid$DEMSRT6, breaks=c(200,250,300,350))
> r <- raster(eberg_grid["CL"])
> image(r, col=c("red","green","blue"))
> ## This works fine; now lets try with a larger raster (>5e5 pixels):
> sp <- SpatialPixelsDataFrame(spsample(eberg_grid, n=1e6, type="regular"),
> data=data.frame(v=runif(1000^2)))
> sp$CL <- cut(sp$v, breaks=c(0.1,0.2,0.3,0.4))
> r2 <- raster(sp["CL"])
> image(r2)
>
> Error in .checkLevels(levels(x)[[1]], value) :
>   new raster attributes (factor values) should be in a data.frame (inside a
> list)
>
> Somehow, image function in the raster package does not want to plot large
> rasters that are of factor type. I've looked at the source code
> (https://r-forge.r-project.org/scm/viewvc.php/pkg/raster/R/image.R?view=markup&root=raster),
> and it looks as the problem is with the "maxpixels" argument (if the new
> raster has >5e5 pixels, the function breaks).
>
> thank you,
>
> T. (Tom) Hengl
> Url: http://www.wageningenur.nl/en/Persons/dr.-T-Tom-Hengl.htm
> Network: http://profiles.google.com/tom.hengl
> Publications: http://scholar.google.com/citations?user=2oYU7S8AAAAJ
>
> _______________________________________________
> R-sig-Geo mailing list
> R-sig-Geo at r-project.org
> https://stat.ethz.ch/mailman/listinfo/r-sig-geo



-- 
Pascal Oettli
Project Scientist
JAMSTEC
Yokohama, Japan