[R-sig-Geo] Clip a raster

[Mayeul KAUFFMANN]

Hi,
Just a comment to sum up: Robert and Johannes mentioned two ways of clipping
that give different results.
My example: clipping MODIS raster data to Democratic Republic of Congo (DRC)

Robert suggested:
MODIS_Drc_cropped<-crop(MODIS, Drc_spdf) # Here, MODIS cropped over a rectangle,
so bigger than AOI

Johannes suggested:
MODIS_Drc_cropped<-crop(MODIS, Drc_spdf)
DRC_mask_raster <- polygonsToRaster(Drc_spdf, raster(MODIS_Drc, values=NA),
  field=-1, updateRaster=TRUE ) # Make a raster mask from DRC area
MODIS_Drc<- mask( MODIS_Drc_cropped, DRC_mask_raster) # apply the masked to the
small rectangle MODIS

MODIS_Drc_cropped is MODIS clipped over a rectangle which is the bounding box of
DRC.
MODIS_Drc has only data within the borders (the rest is NA)

Mayeul
_____________________________________________________
Dr. Mayeul KAUFFMANN, Conflict Specialist
European Commission, Joint Research Centre (JRC)
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Global Security and Crisis Management - ISFEREA
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-----Original Message-----
From: r-sig-geo-bounces at stat.math.ethz.ch
[mailto:r-sig-geo-bounces at stat.math.ethz.ch] On Behalf Of Johannes Signer
Sent: Thursday, October 14, 2010 5:39 PM
To: Manuel Spínola
Cc: r-sig-geo at stat.math.ethz.ch
Subject: Re: [R-sig-Geo] Clip a raster

Hi,

with the raster package you could use: polygons to raster
(?polygonsToRaster), converting the Costa Rica shapefile to a raster
and then use mask (?mask).

Best
Johannes

On Thu, Oct 14, 2010 at 5:16 PM, Manuel Spínola <mspinola10 at gmail.com> wrote:
>  Dear list members,
>
> I download bioclim data in a raster format (estension: .bil) and I would
> like to clip the variables to a ploygon stored as a shapefile (Costa
> Rica outline).
> How can I do that?
>
> I read the raster file like this:
>
> x <- readGDAL("bio1_23.bil")
>
> Thank you very much in advance.
> Best,
>
> Manuel
>
>
> --
> *Manuel Spínola, Ph.D.*
> Instituto Internacional en Conservación y Manejo de Vida Silvestre
> Universidad Nacional
> Apartado 1350-3000
> Heredia
> COSTA RICA
> mspinola at una.ac.cr
> mspinola10 at gmail.com
> Teléfono: (506) 2277-3598
> Fax: (506) 2237-7036
> Personal website: Lobito de río
> <https://sites.google.com/site/lobitoderio/>
> Institutional website: ICOMVIS <http://www.icomvis.una.ac.cr/>
>
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>
>
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