Using a pre-defined NCEP grid from the NCEP ON388 Grid Identification Table, we'll create a latitude band, using the "lat" masking type, for the tropics region. Run Gen-Vx-Mask on the command line using the following command:
G004 \
G004 \
${METPLUS_TUTORIAL_DIR}/output/met_output/gen_vx_mask/G004_Tropics.nc \
-type lat -thresh 'ge-30 && le30'
Most of the grids defined in ON388 Table B can be referenced in MET as "GNNN" where NNN is the 3-digit grid number. Run "ncdump -h" on the output file and notice that the mask variable is named "lat_mask":
lat_mask:long_name = "lat_mask masking region" ;
lat_mask:_FillValue = -9999.f ;
lat_mask:mask_type = "lat>=-30&&<=30" ;
Use the "-name" command line option, as shown below, to override this default.
To compute the intersection or union of two masks, use the output from the first run as input to the second. Run Gen-Vx-Mask on the command line using the following command, which uses the "lon" masking type:
${METPLUS_TUTORIAL_DIR}/output/met_output/gen_vx_mask/G004_Tropics.nc \
${METPLUS_TUTORIAL_DIR}/output/met_output/gen_vx_mask/G004_Tropics.nc \
${METPLUS_TUTORIAL_DIR}/output/met_output/gen_vx_mask/G004_EastPac.nc \
-type lon -thresh 'le-70 && ge-130' -intersection -name EastPac
Compare this intersection output to the union of the two masks, computed below:
${METPLUS_TUTORIAL_DIR}/output/met_output/gen_vx_mask/G004_Tropics.nc \ ${METPLUS_TUTORIAL_DIR}/output/met_output/gen_vx_mask/G004_Tropics.nc \
${METPLUS_TUTORIAL_DIR}/output/met_output/gen_vx_mask/G004_EastPac.nc \
-type lon -thresh 'le-70 && ge-130' -union
Now we'll use the "grid" masking type to select a subgrid from a larger grid. Run Gen-Vx-Mask on the command line using the following command:
G004 \
${METPLUS_DATA}/met_test/data/sample_obs/ST2ml/ST2ml2005080712.Grb_G212 \
${METPLUS_TUTORIAL_DIR}/output/met_output/gen_vx_mask/G004_SUBGRID.nc \
-type grid
On the next page, we'll demonstrate using the "data" and "solar_alt" masking types.
