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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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When the library encounters a value equal to the missing value in the data array, it will set the bitmap entry to 0 for that grid point. For an example see grib_set_bitmap
When decoding, you can directly query the bitmap to discover missing data values. For an example see grib_iterator_bitmap
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