[R-sig-Geo] map algebra with ascii grid

[Tim Keitt]

Any algebraic operation supported by R can easily be applied to a GDAL
image using rgdal -- size is virtually unlimited if you pull in data
as raster lines or tiles. The approach is to create an output image
and then use getRasterData and putRasterData to read chunks of data,
operate on them, and then write back to disk. I can work up an example
if anyone is interested.

THK

On 7/16/07, Denham Robert <Robert.Denham at nrw.qld.gov.au> wrote:
>
> Philip,
>       this sounds like an interesting approach.  Do you do anything in
> particular to handle larger datasets?  How large are your images?
>
> Robert Denham
> Environmental Statistician
> Remote Sensing Centre
> Telephone 07 3896 9899
> www.nrw.qld.gov.au
>
> Department of Natural Resources & Water
> QScape Building, 80 Meiers Road, Indooroopilly Qld 4068
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Sun, 15 Jul 2007 07:40:12 -0600
> From: Philip Riggs <priggs at cnr.colostate.edu>
> Subject: [R-sig-Geo]  map algebra with ascii grid
> To: r-sig-geo at stat.math.ethz.ch
> Message-ID: <3513F1E2-D6E1-4B2B-89E8-D0B00C2804B7 at cnr.colostate.edu>
> Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed
>
> >> Dear R Users,
> >>
> >> could you please advise me on doing map algebra with spatial grids?
> >> It's the first time I am using spatial objects in R. I have imported
> >> an ascii grid file and wanted to round the values in it or sum with a
>
> >> value, but it gives an error message:
> >>
>
> >I use Python with Numpy/GDAL python bindings all the time to do spatial
> algebra and manipulate grids.
> >It has all the math functions, and in the case of categorical data you
> can reassign values. Then I
> >use rpy to do any statistical analyses in R. You could also do your
> manipulation in Python, then
> >save the grid in an appropriate format for import into R to do the
> statistical analyses.
>
> > Philip
>
>
>
>
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-- 
Timothy H. Keitt, University of Texas at Austin
Contact info and schedule at http://www.keittlab.org/tkeitt/
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