| BIT | VALUE | MEANING |
|---|---|---|
| Grid point data | ||
| Spherical Harmonic Coefficients | ||
| Simple packing | ||
| Second order ("Complex") Packing | ||
| Original data were floating point values | ||
| Original data were integer values | ||
| No additional flags at octet 14 | ||
| Octet 14 contains flag bits 5 - 12 | ||
| The following gives the meaning of the bits in octet 14 ONLY if bit 4 is set to 1. Otherwise octet 14 contains regular binary data. | ||
| Reserved (set to 0) | ||
| Single datum at each grid point | ||
| Matrix of values at each grid point | ||
| No secondary bit maps | ||
| Secondary bit maps present | ||
| Second order values have constant width | ||
| Second order values have different widths | ||
| Reserved (set to 0) | ||
| Notes: | |
| 1) | Bit 3 is set to 1 to indicate that the original data were integers; when this is the case any non-zero reference values should be rounded to an integer value prior to placing in the GRIB BDS. |
| 2) | Bit 4 is set to 1 to indicate that bits 5 to 12 are contained in octet 14 of the data section. |
| 3) | Although GRIB is not capable of representing a matrix of data values at each grid point, the meaning of bit 6 is retained in anticipation of a future capability. |
| 4) | When secondary bit maps are present in the data (used in association with second order packing) this is indicated by setting bit 7 to 1. |
| 5) | When octet 14 contains the extended flag information octets 12 and 13 will also contain "special" information; the actual data will begin in a subsequent octet. See above. |
| At present, the "extension" of Table 11 into octet 14 and the associated "advanced" features of GRIB are limited to spherical harmonics and second order("complex") packing in the National Weather Service. Additional variations are included in the WMO Documentation. | |