Octet No. Contents 15 of the Earth (see Code table 3.2) 16 Scale factor of radius of spherical Earth 17–20 Scaled value of radius of spherical Earth 21 Scale factor of major axis of oblate spheroid Earth 22–25 Scaled value of major axis of oblate spheroid Earth 26 Scale factor of minor axis of oblate spheroid Earth 27–30 Scaled value of minor axis of oblate spheroid Earth 31–34 Nx number of points along the x-axis – 35–38 Ny number of points along the y-axis – 39–42 La1 latitude of first grid point – 43–46 Lo1 longitude of first grid point – 47 Resolution and component flags (see Flag table 3.3) 48–51 LatC latitude of the projection center – 52–55 LonC longitude of the projection center – 56–59 Dx x-direction grid length (see Note 1) – 60–63 Dy y-direction grid length (see Note 1) – 64 Projection centre flag (see Flag 3.5) 65 Scanning mode (see Flag table 3.4) Notes: (1) Grid lengths are in of 10-3 m. Within the particular context of the FV3 cubed sphere, it would also be helpful for post-processing purposes to indicate, for each of the 6 projected grids, how they are to be stitched back together to form the original cube surrounding the sphere. Perhaps this could be done by the addition of two new octets to the above template, where the first octet would indicate the total number N of related grids (or, in a sense, The value N would be set equal to 6 in the case of FV3 but could vary for “tiles”?) other potential uses of gnomonic grids, and the second octet would indicate the grid (or number “tile”?) (ranging from 1 to N) being represented within each successive repetition of the template. Assuming it is agreed that this would be a useful and proper feature for inclusion within the proposed GDT, we would certainly welcome other suggestions from experts on alternative ways to accomplish this.
Octet No. Contents 15 of the Earth (see Code table 3.2) 16 Scale factor of radius of spherical Earth 17–20 Scaled value of radius of spherical Earth 21 Scale factor of major axis of oblate spheroid Earth 22–25 Scaled value of major axis of oblate spheroid Earth 26 Scale factor of minor axis of oblate spheroid Earth 27–30 Scaled value of minor axis of oblate spheroid Earth 31–34 Nx – number of points along the x-axis 35–38 Ny – number of points along the y-axis 39–42 La1 – latitude of first grid point 43–46 Lo1 – longitude of first grid point 47 Resolution and component flags (see Flag table 3.3) 48–51 LatC – latitude of the projection center 52–55 LonC – longitude of the projection center 56–59 Dx – x-direction grid length (see Note 1) 60–63 Dy – y-direction grid length (see Note 1) 64 Projection centre flag (see Flag 3.5) 65 Scanning mode (see Flag table 3.4) Notes: (1) Grid lengths are in of 10-3 m. Within the particular context of the FV3 cubed sphere, it would also be helpful for post-processing purposes to indicate, for each of the 6 projected grids, how they are to be stitched back together to form the original cube surrounding the sphere. Perhaps this could be done by the addition of two new octets to the above template, where the first octet would indicate the total number N of related grids (or, in a sense, “tiles”?) The value N would be set equal to 6 in the case of FV3 but could vary for other potential uses of gnomonic grids, and the second octet would indicate the grid (or “tile”?) number (ranging from 1 to N) being represented within each successive repetition of the template. Assuming it is agreed that this would be a useful and proper feature for inclusion within the proposed GDT, we would certainly welcome other suggestions from experts on alternative ways to accomplish this.
IPET-CM-II_Doc2-2-7_GRIB2%20gnomonic%20grid.docx