[R-sig-Geo] raster() not reading in discrete values

[Michael Sumner]

What are the kinds of values that you  see in ArcGIS?  Is this an ADF
raster, i.e. a folder of many files like "w000001.adf" etc. ?

This is a just a guess, so sorry if it's off-base - I don't know of
any non-ESRI tool to get at these values.
If this is an ADF raster I know that you won't be able to access the
descriptive/categorical values you would use in Arc, you'll just get
the underlying integer index.  (BTW, this lookup type with an
underlying integer mapped to a 'descriptive value' is like the factor
type in R - does that sound like what you have?).

The raster is read via the GDAL library, which does not provide the
"categorical values" you assign in Arc. It's just a part of the format
that hasn't been reverse engineered by the GDAL developers, but
further, if your descriptive values are actually text then GDAL cannot
represent them - only numeric types are supported, even though the
rasters in R can have text/character types.

Cheers, Mike.

On Thu, Nov 11, 2010 at 11:35 AM, Tyler Dean Rudolph
<tylerdeanrudolph at gmail.com> wrote:
> I have a pretty simple code to extract cell values from a habitat map
> (RasterLayer) based on xy coordinates.  I recently updated habitat
> information with a new raster image but for some reason now when I read in
> the values it's as though they are no longer being interpreted as discrete
> values, so instead of select, discrete classes I am getting new arbitrary
> groupings that I didn't create.  The input file is a standard
> ArcGIS-configured GRID raster layer.  The attribute table in ArcCatalogue
> displays the data as expected, and I've ensured the raster has been classed
> as containing discrete values prior to opening it in R.
>
> Perhaps something in the packages have changed since I ran this last?  I'm
> currently trying to assess in the raster documentation what kind of
> additional arguments I might have at my disposal in order to clarify how I
> want the data to be read....
>
> Tyler
>
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-- 
Michael Sumner
Institute for Marine and Antarctic Studies, University of Tasmania
Hobart, Australia
e-mail: mdsumner at gmail.com