GRIB section 4, the binary data section

Contents of KSEC4

Element	Contents	GRIB API keys
1	Number of data values in array PSEC4 to be encoded or which have been decoded. When the 'A' coding option is used, the count is the number of image bytes stored four to an integer. When the 'B' coding option is used, the count is the number of integers used to return image bytes, stored four to an integer. When a bitmap is used, this number includes the total of both missing and present data values. If this number is negative: the number of field points is -KSEC4(1), the entire field is missing, all values in PSEC4 are 0, the coded data has all the bits of its scale factor are set to 1 all the bits of the exponent and mantissa of its reference value are set to 1 (This is an ECMWF convention).	numberOfPoints numberOfValues numberOfCodedValues numberOfMissing
2	Number of bits used for each encoded value.	decimalPrecision bitsPerValue
3	Type of data: 0 Grid point data. 128 Spherical harmonic coefficients (Used only if Section 2 is not included when coding data.)	gridType
4	Type of packing: 0 Simple packing. 64 Complex or second-order packing.	packingType = grid_simple | grid_ieee | spectral_complex | spectral_simple | spectral_ieee | grid_simple_matrix | grid_second_order | grid_second_order_different_width | grid_complex | grid_complex_spatial_differencing | grid_jpeg | grid_png | grid_simple_log_preprocessing
5	Data representation: 0 Floating point data. 32 Integer data.
6	Additional flags indicator: 0 No additional flags. 16 Additional flags.
7	Reserved. Set to 0.
8	Number of values indicator: 0 Single datum at each grid point. 64 Matrix of values at each grid point.
9	Secondary bitmaps indicator: 0 No secondary bitmaps. 32 Secondary bitmaps present.
10	Values width indicator: 0 Second order values have constant width. 16 Second order values have different widths.
11	Number of bits for second order values when these have constant width.
12-15	Reserved for WMO reserved flag fields. Set to 0.
16	For complex packing, a pointer to the start of packed data values (ie the octet number). Otherwise set to 0.
17	For complex packing, the scaling factor P, stored as the INTEGER value P*1000 (in the range -10000 to +10000). Otherwise set to 0.
18	For complex packing, the pentagonal resolution parameter J specifying the truncation of the subset of the data represented as 32-bit floating point numbers (ie not packed). Otherwise set to 0.
19	For complex packing, the pentagonal resolution parameter K specifying the truncation of the subset of the data represented as 32-bit floating point numbers (ie not packed). Otherwise set to 0.
20	For complex packing, the pentagonal resolution parameter M specifying the truncation of the subset of the data represented as 32-bit floating point numbers (ie not packed). Otherwise set to 0.
21	The number of non-missing values in a field which uses a bitmap. When the 'B' coding option is used, this count is the number of image bytes (versions of GRIBEX after 13.040).
22-33	Reserved. Set to 0.
34	An offset bit pointer to coded values in the GRIB record. (This is returned by the 'G', 'I' or 'J' decoding options).

X decoding option.

Grid point matrix packing.

ECMWF use of REALs.