[R-sig-Geo] problem with extract() raster package using weight=TRUE

[Robert J. Hijmans]

Umberto,

The work-around is to assure that the CRS are the same:

projection(regioni) <- projection(t500)

You should of course only do that when the projections are in fact the
same, as in this case. The problem is caused by sp::identicalCRS that
compares the verbatim, but not the semantic representation of the CRS
(and, therefore, perhaps should give a warning rather than an error?).

Robert

On Tue, Sep 17, 2013 at 5:10 AM, up <u.p at operamail.com> wrote:
> Hi everybody! I'm a new user, sorry for any kind of errors in posting :-).
>
> I'm trying to use* extract()* from raster library to get data values from
> netcdf file that are inside a shapefile.
> I'm using rgdal library to manage shapefiles, and raster library to read
> netcdf file (a very simple file).
> This is the simple code:
>
>> t500 <-raster("t500.nc")
>> projection(t500)
> [1] "+proj=longlat +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0"
>
>> regioni <- readOGR(".", "ITA_adm1")
> #ITA_adm1 from GADM database of Global Administrative Areas, shapefile
> format
>
>> summary(regioni)
> Object of class SpatialPolygonsDataFrame
> Coordinates:
>         min      max
> x  6.630879 18.52069
> y 35.492917 47.09096
> Is projected: FALSE
> proj4string :
> [+proj=longlat +datum=WGS84 +no_defs +ellps=WGS84 +towgs84=0,0,0]
> (...)
>
>> lombardia <-regioni[regioni$NAME_1=="Lombardia",]
>> liguria <-regioni[regioni$NAME_1=="Liguria",]
>
> Now, I extract values from netcdf file that fall into lombardia:
>
>>extract(t500,lombardia)
> [[1]]
>   [1] 249.3597 249.3362 249.3284 249.9573 249.5706 249.5081 249.4065
> 250.2269
>   [9] 250.2581 250.2151 250.1058 249.9964 249.9261 249.8831 249.8245
> 249.7347
> (...)
>
> Now into liguria:
>
>> extract(t500,liguria)
> [[1]]
>  [1] 249.9729 250.3440 250.2269 250.1800 250.1331 250.0823 250.0198 249.9729
>  [9] 249.9573 249.9651 250.4026 250.3128 250.2425 250.1956 250.0862 250.0550
> [17] 250.0628 250.1019 250.1487 250.4808 250.4222 250.3753 250.2737 250.2972
> [25] 250.3284 250.7972 250.4495 250.4456 250.4495 250.4808 250.8362 250.6800
> [33] 250.5940 250.5862 251.1409 251.0003 250.8753 250.8011 250.7894
>
> Now I try to extract with weight enabled.
>
>> extract(t500,lombardia,weight=T)
> [[1]]
>           value weight
>   [1,] 249.4651   0.23
>   [2,] 249.3948   0.27
>   [3,] 249.8323   0.15
>   [4,] 249.8206   0.42
>   [5,] 249.8206   0.10
>   [6,] 249.4183   0.06
>   [7,] 249.3597   0.99
>   [8,] 249.3362   0.99
>   [9,] 249.3284   0.90
> (...)
>
> Nice one!
> Now I do the same thing on the second shapefile:
>
>> extract(t500,liguria,weight=T)
> Error: identicalCRS(x, y) is not TRUE
>
> That's the problem! I can extract from liguria netcdf values, but I cannot
> extract them with weight.
>
> Any suggestion?
>
> Manymany thanks in advance!
>
> Umberto
>
>
>
> --
> View this message in context: http://r-sig-geo.2731867.n2.nabble.com/problem-with-extract-raster-package-using-weight-TRUE-tp7584665.html
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>
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