[thredds] NetCDF subsetting

• To: thredds@xxxxxxxxxxxxxxxx
• Subject: [thredds] NetCDF subsetting
• From: Kyle Shannon <ksshannon@xxxxxxxxx>
• Date: Tue, 9 Feb 2010 13:06:56 -0700

Hello all,
I am using the netCDF subsetting service on ucar's motherlode thredds
server.  I am having an issue with the projection of the subset.


I run ncdump on the entire ndfd grid (full spatial extents) and get:

kyle@Lucky13:~/nc_issue$ ncdump -h ndfd_all.nc | grep Lambert_Conformal
        Maximum_temperature:grid_mapping = "Lambert_Conformal" ;
    char Lambert_Conformal ;
        Lambert_Conformal:grid_mapping_name = "lambert_conformal_conic" ;
        Lambert_Conformal:standard_parallel = 25. ;
        Lambert_Conformal:longitude_of_central_meridian = 265. ;
        Lambert_Conformal:latitude_of_projection_origin = 25. ;
        Lambert_Conformal:earth_shape = "Earth spherical with radius
specified by producer in m" ;
        Lambert_Conformal:spherical_earth_radius_meters = 6371200. ;
        Lambert_Conformal:GRIB_param_Dx = 5079.361 ;
        Lambert_Conformal:GRIB_param_Dy = 5079.472 ;
        Lambert_Conformal:GRIB_param_GDSkey = 801839731 ;
        *Lambert_Conformal:GRIB_param_La1 = 20.192 ;
        Lambert_Conformal:GRIB_param_LaD = 25. ;
        Lambert_Conformal:GRIB_param_Latin1 = 25. ;
        Lambert_Conformal:GRIB_param_Latin2 = 25. ;
        *Lambert_Conformal:GRIB_param_Lo1 = 238.446 ;
        Lambert_Conformal:GRIB_param_LoV = 265. ;
        Lambert_Conformal:GRIB_param_NpProj = "true" ;
        Lambert_Conformal:GRIB_param_Nx = 1073 ;
        Lambert_Conformal:GRIB_param_Ny = 689 ;
        Lambert_Conformal:GRIB_param_ProjFlag = 0 ;
        Lambert_Conformal:GRIB_param_Quasi = "false" ;
        Lambert_Conformal:GRIB_param_ResCompFlag = 8 ;
        Lambert_Conformal:GRIB_param_SpLat = -90. ;
        Lambert_Conformal:GRIB_param_SpLon = 0. ;
        Lambert_Conformal:GRIB_param_VectorComponentFlag = "gridRelative" ;
        Lambert_Conformal:GRIB_param_Winds = "Relative" ;
        Lambert_Conformal:GRIB_param_grid_name = "Lambert_Conformal" ;
        Lambert_Conformal:GRIB_param_grid_radius_spherical_earth = 6371200.
;
        Lambert_Conformal:GRIB_param_grid_shape = "Earth spherical with
radius specified by producer in m" ;
        Lambert_Conformal:GRIB_param_grid_shape_code = 1 ;
        Lambert_Conformal:GRIB_param_grid_type = 30 ;
        Lambert_Conformal:GRIB_param_grid_units = "m" ;
        Lambert_Conformal:GRIB_param_scanning_mode = 64 ;
        Lambert_Conformal:_CoordinateTransformType = "Projection" ;
        Lambert_Conformal:_CoordinateAxisTypes = "GeoX GeoY" ;

and when I run it on the subsetted data, I get:

kyle@Lucky13:~/nc_issue$ ncdump -h ndfd.nc | grep Lambert_Conformal
        Maximum_temperature:grid_mapping = "Lambert_Conformal" ;
    char Lambert_Conformal ;
        Lambert_Conformal:grid_mapping_name = "lambert_conformal_conic" ;
        Lambert_Conformal:standard_parallel = 25. ;
        Lambert_Conformal:longitude_of_central_meridian = 265. ;
        Lambert_Conformal:latitude_of_projection_origin = 25. ;
        Lambert_Conformal:earth_shape = "Earth spherical with radius
specified by producer in m" ;
        Lambert_Conformal:spherical_earth_radius_meters = 6371200. ;
        Lambert_Conformal:GRIB_param_Dx = 5079.361 ;
        Lambert_Conformal:GRIB_param_Dy = 5079.472 ;
        Lambert_Conformal:GRIB_param_GDSkey = 801839731 ;
        Lambert_Conformal:GRIB_param_La1 = 20.192 ;
        Lambert_Conformal:GRIB_param_LaD = 25. ;
        Lambert_Conformal:GRIB_param_Latin1 = 25. ;
        Lambert_Conformal:GRIB_param_Latin2 = 25. ;
        Lambert_Conformal:GRIB_param_Lo1 = 238.446 ;
        Lambert_Conformal:GRIB_param_LoV = 265. ;
        Lambert_Conformal:GRIB_param_NpProj = "true" ;
        Lambert_Conformal:GRIB_param_Nx = 1073 ;
        Lambert_Conformal:GRIB_param_Ny = 689 ;
        Lambert_Conformal:GRIB_param_ProjFlag = 0 ;
        Lambert_Conformal:GRIB_param_Quasi = "false" ;
        Lambert_Conformal:GRIB_param_ResCompFlag = 8 ;
        Lambert_Conformal:GRIB_param_SpLat = -90. ;
        Lambert_Conformal:GRIB_param_SpLon = 0. ;
        Lambert_Conformal:GRIB_param_VectorComponentFlag = "gridRelative" ;
        Lambert_Conformal:GRIB_param_Winds = "Relative" ;
        Lambert_Conformal:GRIB_param_grid_name = "Lambert_Conformal" ;
        Lambert_Conformal:GRIB_param_grid_radius_spherical_earth = 6371200.
;
        Lambert_Conformal:GRIB_param_grid_shape = "Earth spherical with
radius specified by producer in m" ;
        Lambert_Conformal:GRIB_param_grid_shape_code = 1 ;
        Lambert_Conformal:GRIB_param_grid_type = 30 ;
        Lambert_Conformal:GRIB_param_grid_units = "m" ;
        Lambert_Conformal:GRIB_param_scanning_mode = 64 ;
        Lambert_Conformal:_CoordinateTransformType = "Projection" ;
        Lambert_Conformal:_CoordinateAxisTypes = "GeoX GeoY" ;
        Total_cloud_cover:grid_mapping = "Lambert_Conformal" ;
        Wind_direction_from_which_blowing:grid_mapping = "Lambert_Conformal"
;
        Wind_speed:grid_mapping = "Lambert_Conformal" ;

My question is, how can the latitude and longitude of the 1st cell not
change after the subsetting?  It appears that the meta data from the full
dataset is just copied to the subset data.  Is this correct?  How can I
figure out where my subset data is on the world?

Thanks, sorry for the messy message.

kss
# ===================
Kyle Shannon
Physical Science Technician
RMRS Fire Sciences Lab
Fire, Fuels & Smoke - RWU 4405
5775 Highway 10 W.
Missoula, MT 59808
(406) 829-6954
kshannon@xxxxxxxxx
# ===================

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