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Sub-area Extraction from a Fieldset

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The GRIB Filter icon also allows the extraction of a sub-area from a fieldset. Create a new one and, using the Area parameter, extract just the data over a selected region for any of the supplied GRIB files. The area is defined as a list of 4 numbers, forward slash-delimited, representing the its North/West/South/East coordinates of the areabounds.

Conversion Between Fields and Points

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Metview provides two icons, Geopoints To Grib and Grib To Geopoints for the purpose of converting between GRIB (gridded) and geopoints (scattered) formats.

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Plot the results and cross-reference with the original result of 6 fields to confirm that you understand what has been computed.

Automatic conversion between grids

Write some macro code which automatically converts t2m_forecast.grib to use the same grid as the first field in uv850.grib. Hints:

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• use the Grib Examiner to find which GRIB_API keys define these parameters

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Extract field values at a set of locations

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There are many ways to extract the value of a field at a given point or set of points. Try this one - call nearest_gridpoint_info ( fieldset,number,number ) with the latitude and longitude of a geographical location and print the result to see which data gridpoint is closest to it.

Automatic conversion between grids

Write some macro code which automatically converts t2m_forecast.grib to use the same grid as the first field in uv850.grib. Hints:

• read both files
• use the grib_get_double(fieldset, string) function twice to extract the grid resolution from the first field in uv850 (uv850[1])
  • use the Grib Examiner to find which GRIB_API keys define these parameters
• use the read() command to set the grid on the temperature field