[R-sig-Geo] extract values to points

[Paul Hiemstra]

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]]
>>>
>>> _______________________________________________
>>> R-sig-Geo mailing list
>>> R-sig-Geo at stat.math.ethz.ch
>>> 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
>>
>> _______________________________________________
>> R-sig-Geo mailing list
>> R-sig-Geo at stat.math.ethz.ch
>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>>     
>
>
> --
> 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