
Dear list,

thank you very much for all the many suggestions on how to extract values to points! I ended up using the RSAGA package with the pick.from.ascii.grid() function.

Cheers,
Frauke

> Date: Tue, 10 Mar 2009 20:19:17 +0800
> Subject: Re: [R-sig-Geo] extract values to points
> From: r.hijmans@gmail.com
> To: p.hiemstra@geo.uu.nl
> CC: ksafi@mail.orn.mpg.de; r-sig-geo@stat.math.ethz.ch; fkbarthold46@hotmail.com
> 
> Just for the record. this is how I would do this with the raster
> package (Kamran's example should work, but seems a bit unnecessarily
> complex; just what we are trying to avoid with that package :):
> 
> install.packages("raster", repos="http://R-Forge.R-project.org")
> library(raster)
> 
> xy <- your matrix
> raster <- rasterFromFile("C:/yourfile")
> v <- xyValues(raster, xy)
> 
> xyv <- cbind(xy, v)
> 
> Robert
> 
> On Tue, Mar 10, 2009 at 7:50 PM, Paul Hiemstra <p.hiemstra@geo.uu.nl> wrote:
> > Hi,
> >
> > Funny to see how you can do things in multiple ways in R :). To add to the
> > possibilities, you could probably also get this functionality using R and
> > Grass.
> >
> > I would personally recommend to use overlay() as you don't have to install
> > anything apart from the sp package, unlike using rsaga and SAGA. Especially
> > if the only thing you want is to do an overlay. When there was other SAGA
> > specific functionality you needed, SAGA would be a good option. In addition
> > to not having to install a lot of software, overlay() has been used
> > extensively, this in contrast to the raster package which is still
> > experimental. But this is strictly my personal opinion ofcourse :).
> >
> > cheers,
> > Paul
> >
> > Kamran Safi Radolfzell wrote:
> >>
> >> Hi all,
> >>
> >> the raster package is although in its alpha stage very helpful in this
> >> respect:
> >>
> >> install.packages("raster", repos="http://R-Forge.R-project.org")
> >> library(raster)
> >> library(maptools)
> >> X <- Y <- raster <- rasterFromFile("C:/yourfile")
> >> (result <- data.frame(Long=x, Lat=y, Value=xyValues(raster, matrix(c(x,y),
> >> ncol=2)))))
> >>
> >>
> >> That should work. Remember to take out the install.package after initial
> >> install. Of course you can work with several coordinates. Peadagogically
> >> better is the overlay() function...
> >>
> >> Very straight forward.
> >> Kami
> >>
> >> On Tue, 10 Mar 2009 11:04:23 +0100, Paul Hiemstra wrote
> >>
> >>>
> >>> Hi,
> >>>
> >>> An option using only R is to use the overlay() command from the sp
> >>> package, try running this example:
> >>>
> >>> # Load data
> >>> library(sp)
> >>> data(meuse)
> >>> # point data
> >>> coordinates(meuse) = ~x+y
> >>> data(meuse.grid)
> >>> # grid data
> >>> gridded(meuse.grid) = ~x+y
> >>>
> >>> overlay(meuse.grid, meuse)
> >>> # Returns the indices in meuse.grid correpsonding to the points in meuse
> >>> # get the data from meuse.grid, for example the column "dist"
> >>> # a non spatial vector
> >>> dist = meuse.grid$dist[overlay(meuse.grid, meuse)]
> >>> # A spatialPointsDataFrame
> >>> dist = meuse.grid[overlay(meuse.grid, meuse), "dist"]
> >>>
> >>> Also check out the rgdal pacakge to get your data into R-spatial objects.
> >>>
> >>> cheers,
> >>> Paul
> >>>
> >>> Frauke Barthold wrote:
> >>>
> >>>>
> >>>> Dear list,
> >>>>
> >>>> I have a soilmap as an Ascii grid and a dataframe with x and y
> >>
> >> coordinates (these are sampling points). I would now like to extract
> >> values from the soilmap to the dataframe based on location, the  x and y
> >> values. Is there any way to do this in R?
> >>
> >>>>
> >>>> Cheers,
> >>>> Frauke
> >>>> _________________________________________________________________
> >>>>
> >>>>
> >>>>        [[alternative HTML version deleted]]
> >>>>
> >>>> _______________________________________________
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> >>>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
> >>>>
> >>>>
> >>>
> >>> --
> >>> Drs. Paul Hiemstra
> >>> Department of Physical Geography
> >>> Faculty of Geosciences
> >>> University of Utrecht
> >>> Heidelberglaan 2
> >>> P.O. Box 80.115
> >>> 3508 TC Utrecht
> >>> Phone:  +3130 274 3113 Mon-Tue
> >>> Phone:  +3130 253 5773 Wed-Fri
> >>> http://intamap.geo.uu.nl/~paul
> >>>
> >>> _______________________________________________
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> >>>
> >>
> >>
> >> --
> >> Open WebMail Project (http://openwebmail.org)
> >>
> >>
> >
> >
> > --
> > Drs. Paul Hiemstra
> > Department of Physical Geography
> > Faculty of Geosciences
> > University of Utrecht
> > Heidelberglaan 2
> > P.O. Box 80.115
> > 3508 TC Utrecht
> > Phone:  +3130 274 3113 Mon-Tue
> > Phone:  +3130 253 5773 Wed-Fri
> > http://intamap.geo.uu.nl/~paul
> >
> > _______________________________________________
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> > R-sig-Geo@stat.math.ethz.ch
> > https://stat.ethz.ch/mailman/listinfo/r-sig-geo
> >

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