[R-sig-Geo] How to pick up cell values of grids using points?

[Paul Hiemstra]

Hi,

Have a look at the overlay() function in the sp-package.

cheers,
Paul

Yong Li wrote:
> Hi ALL,
>
> I want to pick up cells values of a grid (say a RS image) using points' positions. For example, I have an image and a point shape file with the same coordinate system, then I try to overlay points on the image, and want to get the cell values of the on-point cell and 8 surrounding cells. Could any expert give some tips to solve my problem?
>
> Regards
>
> Yong
>
>
>
> -----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 r-sig-geo-request at stat.math.ethz.ch
> Sent: 2008年12月3日 22:00
> To: r-sig-geo at stat.math.ethz.ch
> Subject: R-sig-Geo Digest, Vol 64, Issue 3
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> Today's Topics:
>
>    1. GSTAT: Optimize power value for IDW (Zev Ross)
>    2. Re: GSTAT: Optimize power value for IDW (Paul Hiemstra)
>    3. R: GSTAT: Optimize power value for IDW (Paul Hiemstra
>       approach) (Alessandro)
>    4. Re: R: GSTAT: Optimize power value for IDW (Paul Hiemstra
>       approach) (Zev Ross)
>    5. Re: R: GSTAT: Optimize power value for IDW (Paul Hiemstra
>       approach) (Edzer Pebesma)
>    6. Raster file from ascii file and flattening Africa ....	:)
>       (Corrado)
>    7. Re: Raster file from ascii file and flattening Africa	....:)
>       (Kamran Safi)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Tue, 02 Dec 2008 13:59:47 -0500
> From: Zev Ross <zev at zevross.com>
> Subject: [R-sig-Geo] GSTAT: Optimize power value for IDW
> To: r-sig-geo at stat.math.ethz.ch
> Message-ID: <493585A3.2040909 at zevross.com>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> Hi All,
>
> ArcGIS has a nice little button that calculates the optimal power value 
> to use for inverse distance weighting based on cross-validation and 
> RMSPE. Just wondering if anyone had written something similar in R -- 
> I'm using GSTAT and I'd like to avoid back and forth with ArcGIS (and 
> obviously I'd like to avoid writing it myself as well!).
>
> Zev
>
>   


-- 
Drs. Paul Hiemstra
Department of Physical Geography
Faculty of Geosciences
University of Utrecht
Heidelberglaan 2
P.O. Box 80.115
3508 TC Utrecht
Phone: 	+31302535773
Fax:	+31302531145
http://intamap.geo.uu.nl/~paul