Content from 

https://confluence-test.ecmwf.int/display/ECC/Frequently+Asked+Questions

Summary

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  grib_to_netcdf: skips Control Forecast when I convert Ensemble Forecast data - ecCodes GRIB FAQ —

  If you have a file with both Control and Perturbed forecasts, grib_to_netcdf will only convert the pf. Normally from 51 members in the GRIB file, only 50 appear in the netCDF.

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  grib_to_netcdf: Why do I get the error "Wrong number of fields... Try using the -T option" - ecCodes GRIB FAQ —

  You try to retrieve data from the ECMWF data archive in netCDF format but the retrieval fails with this message

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  Why do I get a bitmap even though none of my values are missing - ecCodes GRIB FAQ —

  If you encode data in a GRIB message and none of the values are actually missing, you can still end up with a Bitmap Section.

  Step-by-step guide

  If you encode data in GRIB and set the key "bitmapPresent" to 1, you will get a Bitmap Section in your message. If none of the values encoded match the "missingValue" key (by default 9999) then you will end up with a bitmap with all entries being 1 (data is present). This can add weight to the message (There is a single bit for each data value, therefore a data array of N points requires N/8 bytes for the bitmap array).

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  What is the GRIB bitmap - ecCodes GRIB FAQ —

  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.

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  What happens when I set the packingType to grid_jpeg on a GRIB1 message - ecCodes GRIB FAQ —

  Actually nothing! JPEG packing is not supported for GRIB edition 1 but rather than fail, the library leaves the message as is.

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  Issues converting from grid_complex_spatial_differencing to simple packing - ecCodes GRIB FAQ —

  This article relates to GRIB edition 2

  There are GRIB messages whose packingType is "grid_complex_spatial_differencing" where the missing values are not in a bitmap but stored in the Data Section (as coded values).
  In these cases conversion to simple packing can fail.

  A workaround is to set the key "bitmapPresent" to 1 before the conversion. This ensures a bitmap is created for the output GRIB and the missing values correctly stored:

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  How do I use an OR condition (logical disjunction) in a where clause - ecCodes GRIB FAQ —

  For example in grib_get you may want to show all messages which have a level of 100, 150 or 200.

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  Creating your own local definitions - ecCodes GRIB FAQ —

  Local definitions are required when one needs to store information which is not part of the standard GRIB header. This might be local parameters or local definitions.

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  How can I find out which keys can be set to "missing" - ecCodes GRIB FAQ —

  If you take the sample GRIB file "GRIB2.tmpl" and dump it, you can see which keys are MISSING (i.e., their values are all 1's) but it is not possible to see which keys can be MISSING. So for example take the key "iDirectionIncrement":

  % grib_dump -O GRIB2.tmpl
  ...
  iDirectionIncrement = 2000000
  ...

  So in this case its value is not MISSING but it is possible for this value to be MISSING. This is not indicated here. 

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  How can I set the verbosity level to see debug output? - ecCodes FAQ —

  There is an environment variable called ECCODES_DEBUG: If set to -1, it will enable brief debug-level logging messages to be displayed by the library. If set to 1, you will get very verbose output.

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  How do I set the product definition template in a GRIB2 message - ecCodes GRIB FAQ —

  Let's say you want your message to use the product definition template 40 (The full list is defined in Code table 4.0):

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  How do I know if I am dealing with a multi-field GRIB file - ecCodes GRIB FAQ —

  The only possible way of detecting if a GRIB file is multi-field is by using the grib tools or the API to turn the support for multiple fields in a single GRIB message on or off and observe the results

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  How can I get verbose output when running tests with ctest - ecCodes FAQ —

  When you run the tests via CMake (which actually runs ctest), you are only told if it passed or failed. After a failure you want to re-run the test and see all of what the test was doing.

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  How can I multiply the field values by a constant - ecCodes GRIB FAQ —

  One way is to use grib_set with the key "scaleValuesBy".  Let's say you have a field in orig.grib whose values you want to multiply by 2.1. First check the original data value statistics

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  How can I remove the PV array (list of vertical coordinates) - ecCodes GRIB FAQ —

  his can be done by setting the key "deletePV" as shown:

  % grib_set -s deletePV=1 in.grib out.grib