[R-sig-Geo] How to subset a spatial grid?

[Roger Bivand]

On Tue, 20 May 2008, Edzer Pebesma wrote:

> Yong, I would have loved to see your R shaking.

Unless you do seismology, of course?

>
> This argument has been heard more often here. When processing massive grids, 
> please have a look at the function getRasterData in package rgdal. It allows 
> you to _read_ only portions of a grid.

This is the best current way to do things certainly, especially when many 
bands/variables are involved. What I'm wondering is whether a class could 
be written with an SQLiteDF sqlite.data.frame in the data slot? There is a 
talk at useR! on a proposed SQLiteMap, but for vector data, and which 
appears to miss sp classes, so I don't think that it is relevant.

Roger

> --
> Edzer
>
> Yong Li wrote:
>>  Thanks Edzer and Hengl. It works.
>>  But R is really shaking when large grids are processed. We wish there is
>>  improvement of sp in the future like GIS handling grids.
>>
>>  Regards
>>
>>  Yong
>>
>>  ------------------------------------------------------------------------
>>  *From:* Edzer Pebesma [mailto:edzer.pebesma at uni-muenster.de]
>>  *Sent:* Tue 20/05/2008 6:11 PM
>>  *To:* Yong Li
>>  *Cc:* r-sig-geo at stat.math.ethz.ch
>>  *Subject:* Re: [R-sig-Geo] How to subset a spatial grid?
>>
>>  Have you tried
>>
>>  Map1 <- Map[1:100,1:100]
>>  ?
>>
>>  Note that this works differently for SpatialGridDataFrames and
>>  SpatialPixelsDataFrames; the first knows about [rows,cols,bands], the
>>  second about [pixels, bands].
>>  --
>>  Edzer
>>
>>  Yong Li wrote:
>> >  Dear All,
>> > 
>> >  I want to subset a large spatial grid (2000*2000) into many smaller
>> >  grids for further processing in my simulation models. Could anyone do it
>> >  before and any tips will be highly appreciated?
>> > 
>> >  Library(rgdal)
>> >  Map <- readGDAL("yong.img")  # one image from erdras imagine
>> >  Map$va <- Map$band1
>> >  Map$band1 <- NULL
>> > ????
>> >  Map1 <- a subset of Map$va based on selected cols and rows.
>> > ????......
>> > 
>> >  Cheers
>> > 
>> >  Yong Li
>> > 
>> > _______________________________________________
>> >  R-sig-Geo mailing list
>> >  R-sig-Geo at stat.math.ethz.ch
>> >  https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>> > 
>> 
>
> _______________________________________________
> R-sig-Geo mailing list
> R-sig-Geo at stat.math.ethz.ch
> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>

-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no