The bitmap is an array of binary values. Its purpose is to indicate the presence or absence of data at each of the grid points. A value of '0' means data is missing and a '1' means data is present.
Note: The bitmap section is optional. If it is not present, it means every grid point has an associated value.
In order to conserve space, the bitmap is used to efficiently indicate those data points that actually appear in the Data Section.
Bitmap
| 0 | 0 | 0 | 0 |
| 0 | 1 | 1 | 0 |
| 0 | 0 | 1 | 0 |
Encoded data
| 2.5 | 4.6 | ||
| 9.1 |
In the example shown above, we have 12 grid points of which 3 have actual 'real' values which are {2.5, 4.6, 9.1}.
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| Note |
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The value of the "missingValue" key used to encode the data is not itself encoded in the GRIB.The data encoder can use, say, missingValue=9999 to encode the data while the data decoder can use missingValue=1111 when decoding. |
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