[R-sig-Geo] gdal color tables

[Barry Rowlingson]

How to create colour-paletted rasters using R and Python:

http://www.rpubs.com/geospacedman/rasterColourPalettes

It would be great to be able to do this solely from R using either
raster or rgdal, and to have the couple of bugs with paletted rasters
in package:raster mentioned in the Rpubs doc fixed. I shall try and
raise this with Robert H when everyone comes out of hibernation in
January.

On Sun, Dec 23, 2012 at 9:51 PM, Rowlingson, Barry
<b.rowlingson at lancaster.ac.uk> wrote:
> Here's a solution:
>
> makePalette <- function(colourvector){
>   cmat = cbind(t(col2rgb(colourvector)),255)
>   res = apply(cmat,1,function(x){sprintf('<Entry c1="%s" c2="%s"
> c3="%s" c4="%s"/>',x[1],x[2],x[3],x[4])})
>   res = paste(res,collapse="\n")
>   res
> }
>
>
> Then:
>
>  write a raster tiff
>
>  writeRaster(iom,"test.tif",overwrite=TRUE,datatype="INT1U")
>
>
> Then use makePalette to create the colortable lines:
>
> cat(makePalette(iom at legend@colortable)) # replace
> iom at legend@colortable with your colour table vector
>
> That spits out a bunch of <Entry> lines. Stick them in your .vrt file thus:
>
> <VRTDataset rasterXSize="413" rasterYSize="397">
>   <VRTRasterBand dataType="Byte" band="1">
>     <ColorInterp>Palette</ColorInterp>
> <SimpleSource>
> <SourceFilename relativeToVRT="1">test.tif</SourceFilename>
> </SimpleSource>
>     <ColorTable>
> <Entry c1="0" c2="0" c3="0" c4="255"/>
> <Entry c1="230" c2="0" c3="77" c4="255"/>
> <Entry c1="255" c2="0" c3="0" c4="255"/>
> <Entry c1="204" c2="77" c3="242" c4="255"/>
> <Entry c1="204" c2="0" c3="0" c4="255"/>
> [etc]
>    </ColorTable>
>   </VRTRasterBand>
> </VRTDataset>
>
> Note you have to fill in the rasterXSize and rasterYSize, and the
> source filename. Also you'll need to get the geotransform of the
> original and stick that in otherwise your raster is geolocated at
> (1:Nrows, 1:Ncolumns).
>
> If I do all that, I get a raster created by R that I can read into
> QGis and is coloured according to my colour scheme, as long as I open
> *test.vrt* in QGis and *not* test.tif.
>
> I'm sorry this isn't (yet) a one-shot solution, and its a bit of a
> construction set. Like I said, two minute job, twenty minute job to do
> properly... I've spent ten minutes on it :)
>
> Barry
>
>
>
>
> On Sun, Dec 23, 2012 at 9:25 PM, Rowlingson, Barry
> <b.rowlingson at lancaster.ac.uk> wrote:
>> On Sun, Dec 23, 2012 at 8:23 PM, Roger Bivand <Roger.Bivand at nhh.no> wrote:
>>
>>> There is no support in raster or sp objects for symbology, and unless
>>> someone extends the classes to accommodate symbology on a dynamic
>>> by-attribute basis, it isn't going to happen.
>>>
>>
>>  I'm not sure that's true - I can read in a raster from a geoTIFF and
>> get a colour table from it, then plot will show it with the right
>> colours - here's a Land Use tiff:
>>
>>> lu
>> class       : RasterLayer
>> dimensions  : 397, 413, 163961  (nrow, ncol, ncell)
>> resolution  : 100, 100  (x, y)
>> extent      : 3356200, 3397500, 3533200, 3572900  (xmin, xmax, ymin, ymax)
>> coord. ref. : +proj=laea +lat_0=52 +lon_0=10 +x_0=4321000 +y_0=3210000
>> +ellps=GRS80 +units=m +no_defs
>> data source : /data/rowlings/MapLibrary/Europe/UK/IsleOfMan/iomcorine.tiff
>> names       : iomcorine
>> values      : 0, 255  (min, max)
>>
>>> lu at legend@colortable[1:10]
>>  [1] "#000000" "#E6004D" "#FF0000" "#CC4DF2" "#CC0000" "#E6CCCC" "#E6CCE6"
>>  [8] "#A600CC" "#A64D00" "#FF4DFF"
>>
>>
>>  Support for this is minimal in package:raster, and I think what Agus
>> is trying to do (correct me if wrong) is create a raster with a colour
>> table such as this from R. If I just use writeRaster I get a numeric
>> raster with no palette.
>>
>> I think Robert has talked about better support for paletted rasters in the past.
>>
>> Barry
>>
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>
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