[R-sig-Geo] Set up raster data in WRF Mercator projection

[Dominik Schneider]

did you see this thread? might help:
http://r-sig-geo.2731867.n2.nabble.com/adapting-spatial-points-and-wrld-smpl-to-a-reference-system-implicit-in-a-nc-file-tt7589570.html

>From my notes, the mercator WRF projection would look like this:
Projection_String = ('PROJCS["Sphere_Mercator",'
                             'GEOGCS["GCS_Sphere",'
                             'DATUM["D_Sphere",'
                             'SPHEROID["Sphere",6370000.0,0.0]],'
                             'PRIMEM["Greenwich",0.0],'
                             'UNIT["Degree",0.0174532925199433]],'
                             'PROJECTION["Mercator"],'
                             'PARAMETER["False_Easting",0.0],'
                             'PARAMETER["False_Northing",0.0],'
                             'PARAMETER["Central_Meridian",' +
str(central_meridian) + '],'
                             'PARAMETER["Standard_Parallel_1",' +
str(standard_parallel_1) + '],'
                             'UNIT["Meter",1.0]]')


where central_meridian = STAND_LON and standard_parallel_1=TRUELAT1

so to start I think you want (changes in *bold*):
"+proj=merc +lat_ts=30 +lon_0=*290* +a=6370000.0 +b=6370000.0 +units=*m*
 +no_defs")

if you post the data, someone might be able to help create a proper raster
for you.


On Wed, Aug 3, 2016 at 9:46 AM, David Wang <dw2116 at outlook.com> wrote:

> Hello,
>
>
> I'd like to load a WRF (Weather Research and Forecasting) output file in
> NetCDF as rasters and set up correct projection and coordinates. Using land
> mask as an example,
>
>
> landmask <- raster("geo_em_d01.nc", varname = "LANDMASK")
>
>
> The projection of this particular WRF simulation is Mercator. After
> extensive googling, I came up with this projection string:
>
>
> projection(landmask) <- CRS("+proj=merc +lat_ts=30 +lon_0=-67 +a=6370000.0
> +b=6370000.0 +units=km +no_defs")
>
>
> That is based on the grid information from ncdump -h geo_em_d01.nc:
>
>
>                 :GRIDTYPE = "C" ;
>                 :DX = 27000.f ;
>                 :DY = 27000.f ;
>                 :DYN_OPT = 2 ;
>                 :CEN_LAT = 32.f ;
>                 :CEN_LON = -67.f ;
>                 :TRUELAT1 = 30.f ;
>                 :TRUELAT2 = 45.f ;
>                 :MOAD_CEN_LAT = 32.f ;
>                 :STAND_LON = 290.f ;
>                 :POLE_LAT = 90.f ;
>                 :POLE_LON = 0.f ;
>                 :corner_lats = 6.033165f, 52.29568f, 52.29568f, 6.033165f,
> 6.033165f, 52.29568f, 52.29568f, 6.033165f, 5.893715f, 52.38135f,
> 52.38135f, 5.893715f, 5.893715f, 52.38135f, 52.38135f, 5.893715f ;
>                 :corner_lons = -129.8151f, -129.8151f, -4.184856f,
> -4.184856f, -129.9554f, -129.9554f, -4.044647f, -4.044647f, -129.8151f,
> -129.8151f, -4.184856f, -4.184856f, -129.9554f, -129.9554f, -4.044647f,
> -4.044647f ;
>                 :MAP_PROJ = 3 ;
>
> However, I'm not entirely sure this projection is correct. Furthermore, I
> have no clue how to set extent(landmask) in km. Can anyone familiar with
> WRF give me a pointer or two?
>
>
> Thanks,
>
> David
>
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>
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