Per #2118, I found a reference in ECMWF documentation for specifying …

…rotated lat/lon grids in GRIB1. https://apps.ecmwf.int/codes/grib/format/grib1/grids/10/ These changes update the MET code to parse location of the south pole and auxiliary rotation. I double-checked in wgrib and see the exact same processing for rotated lat/lon GRIB1 files. So I'm confident in the approach. While it would be preferable to have additional sample data for testing, it's no longer a requirement for this bugfix.
dtcenter · Apr 6, 2022 · ec295a9 · ec295a9
1 parent b368ad1
commit ec295a9
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Showing 3 changed files with 36 additions and 6 deletions.
diff --git a/met/src/libcode/vx_data2d_grib/grib_classes.cc b/met/src/libcode/vx_data2d_grib/grib_classes.cc
@@ -1874,6 +1874,27 @@ else if ((h.type == 5))
 
    file << "   scan_flag:  " << (int) h.grid_type.stereographic.scan_flag      << "\n\n";
 }
+else if ((h.type == 10))
+{
+
+   file << "   lat1:      " << char3_to_int(h.grid_type.rot_latlon_grid.lat1)     << "\n";
+   file << "   lon1:      " << char3_to_int(h.grid_type.rot_latlon_grid.lon1)     << "\n";
+
+   file << "   res_flag:  " << (int) h.grid_type.rot_latlon_grid.res_flag         << "\n";
+
+   file << "   lat2:      " << char3_to_int(h.grid_type.rot_latlon_grid.lat2)     << "\n";
+   file << "   lon2:      " << char3_to_int(h.grid_type.rot_latlon_grid.lon2)     << "\n";
+
+   file << "   di:        " << char2_to_int(h.grid_type.rot_latlon_grid.di)       << "\n";
+   file << "   dj:        " << char2_to_int(h.grid_type.rot_latlon_grid.dj)       << "\n";
+
+   file << "   scan_flag: " << (int) h.grid_type.rot_latlon_grid.scan_flag        << "\n";
+
+   file << "   lat_sp:    " << char3_to_int(h.grid_type.rot_latlon_grid.lat_sp)   << "\n";
+   file << "   lon_sp:    " << char3_to_int(h.grid_type.rot_latlon_grid.lon_sp)   << "\n";
+
+   file << "   rotation:  " << char4_to_dbl(h.grid_type.rot_latlon_grid.rotation) << "\n\n";
+}
 
 return ( file );
 

diff --git a/met/src/libcode/vx_data2d_grib/grib_classes.h b/met/src/libcode/vx_data2d_grib/grib_classes.h
@@ -181,6 +181,8 @@ struct LatLon {                              //   Latitude/Longitude Grid
 
 };
 
+   // Reference: https://apps.ecmwf.int/codes/grib/format/grib1/grids/10
+
 struct RotLatLon {                           //   Rotated Latitude/Longitude Grid
 
    unsigned char         lat1[3];            //   11 - 13
@@ -196,7 +198,12 @@ struct RotLatLon {                           //   Rotated Latitude/Longitude Gri
 
    unsigned char       scan_flag;            //   28
 
-   unsigned char       unused[14];           //   29 - 42
+   unsigned char        unused[4];           //   29 - 32
+
+   unsigned char        lat_sp[3];           //   33 - 35
+   unsigned char        lon_sp[3];           //   36 - 38
+
+   unsigned char      rotation[4];           //   39 - 42
 
 };
 

diff --git a/met/src/libcode/vx_data2d_grib/grib_utils.cc b/met/src/libcode/vx_data2d_grib/grib_utils.cc
@@ -352,13 +352,15 @@ if ( ! all_bits_set(gds.grid_type.rot_latlon_grid.di, 2) )  {
 
 }
 
-   // Location of (rotated) south pole and auxiliary rotation hard-coded to 0
+   // Location of (rotated) south pole
+data.true_lat_south_pole =
+   decode_lat_lon(gds.grid_type.rot_latlon_grid.lat_sp, 3);
 
-data.true_lat_south_pole = -90.0;
+data.true_lon_south_pole =
+   -1.0*rescale_lon(decode_lat_lon(gds.grid_type.rot_latlon_grid.lon_sp, 3));
 
-data.true_lon_south_pole = 0.0;
-
-data.aux_rotation = 0.0;
+  // Auxiliary rotation
+data.aux_rotation = char4_to_dbl(gds.grid_type.rot_latlon_grid.rotation);
 
 data.dump();