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Some key names are built from the official WMO documentation on the GRIB edition 1 and edition 2 coding standard removing the spaces in the key description and capitalizing the initials so that the caption:
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There are two different types of keys: coded and computed.
The coded keys are directly linked to octets of the GRIB message and their value is obtained by only decoding the octets. A list of all the coded keys in a message can be obtained using grib_dump without any option (use the -a option to obtain also their aliases).
The computed keys are obtained by combining other keys (coded or computed) and when their value is set all the related keys are set in a cascade process.
These keys provide a synthesis of the information contained in the GRIB message and are a safe way to set complex attributes such as the type of grid or the type of packing. They are also helpful in the interpretation of some octets such as the scanning mode whose bits are related to the way of scanning the grid. In this case the computed keys:
| Code Block | ||
|---|---|---|
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iScansNegatively jScansPositively jPointsAreConsecutive alternativeRowScanning (available only for edition 2) |
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Moreover there are some computed keys that cannot be "get" and can be considered as functions acting on the grib GRIB message in some way. These keys are always characterised by a predicate in their name (e.g. setDecimalPrecision, setBitsPerValue).
For the computed keys we provide the following preliminary documentation that will be extended soon.
MARS keywords
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All MARS keywords are available. Some examples are:
- date
- param
- levtype
- levelist
- step
- stream
- class
Angles in degrees
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All the angle variables are provided in two versions, a native one with the units coded into the GRIB file and an edition-independent one in degrees. It is always better to work with the "in degrees" version that is always provided through the key which has the same name of the native version with the suffix "InDegrees":
| Code Block |
|---|
longitudeOfFirstGridPoint -> longitudeOfFirstGridPointInDegrees latitudeOfFirstGridPoint -> latitudeOfFirstGridPointInDegrees longitudeOfLastGridPoint -> longitudeOfLastGridPointInDegrees latitudeOfFirstGridPoint -> latitudeOfLastGridPointInDegrees latitudeOfFirstGridPoint -> latitudeOfFirstGridPointInDegrees iDirectionIncrement -> iDirectionIncrementInDegrees jDirectionIncrement -> jDirectionIncrementInDegrees |
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- For both editions:
- regular_ll
- reduced_ll
- mercator
- lambert
- polar_stereographic
- UTM
- simple_polyconic
- albers
- miller
- rotated_ll
- stretched_ll
- stretched_rotated_ll
- regular_gg
- rotated_gg
- stretched_gg
- stretched_rotated_gg
- reduced_gg
- sh
- rotated_sh
- stretched_sh
- stretched_rotated_sh
- space_view
- For edition 2 only:
- triangular_grid
- equatorial_azimuthal_equidistant
- lambert_azimuthal_equal_area
- azimuth_range
- cross_section
- Hovmoller
- time_section
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- For GRIB edition 1:
- grid_simple
- grid_simple_matrix
- grid_simple_matrix_bitmap
- grid_second_order
- spectral_complex
- spectral_simple
- For GRIB edition 2:
- grid_simple grid_simple_matrix
- grid_simple_matrix_bitmap
- grid_complex
- grid_complex_spatial_differencing
- grid_jpeg
- grid_ccsds
- grid_second_order
- grid_png
- grid_ieee
- spectral_simple
- spectral_complex
- grid_simple_log_preprocessing
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is a function key used to set the decimal precision see . See the grib_set page for usage.
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