[R-sig-Geo] extract values to points

[Robert Hijmans]

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 at 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
>>>> _________________________________________________________________
>>>>
>>>>
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>>>>
>>>
>>> --
>>> 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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>>
>>
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>
>
> --
> 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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