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Libcf – A CF Convention Library for NetCDF

Ed Hartnett Unidata Program Center Boulder Colorado June 11, 2007. Libcf – A CF Convention Library for NetCDF. Mission : To provide data, tools, and community leadership for enhanced Earth-system education and research. Unidata. NetCDF/libcf Development in C/C++/Fortran at Unidata.

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Libcf – A CF Convention Library for NetCDF

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  1. Ed Hartnett Unidata Program Center Boulder Colorado June 11, 2007 Libcf – A CF Convention Library for NetCDF

  2. Mission : To provide data, tools, and community leadership for enhanced Earth-system education and research. Unidata

  3. NetCDF/libcf Development in C/C++/Fortran at Unidata • NetCDF 3.6.2 released March, 2007 • NetCDF 4.0 beta1 released April 2007 • Libcf alpha4 released November 2006

  4. The NetCDF Classic Model • The netCDF classic data model: files, dimensions, variables, attributes, 6 data types. • The expanded netCDF-4 data model adds: groups, additional atomic and user-defined data types, additional unlimited dimensions. • Create netCDF-4/HDF5 files which conform to the classic model with a flag at create time.

  5. Goals for libcf • Make using CF Convetions easier for readers and writers of data. • Reduce duplication of effort. • Ensure CF conforming files. • Provide a geo-science API for netCDF. • Provide some of the advanced features developed for netCDF-Java. • Work with both netCDF-3 and netCDF-4/HDF5 files.

  6. Limitations of libcf • Handles classic model netCDF only. • Lightly tested. • Doesn't handle indirect coordinates. • Does not check standard name table. • Alpha release - Functions in the API may change a little.

  7. Current Status of libcf • Available in alpha release from libcf web page at Unidata: http://www.unidata.ucar.edu/software/libcf/ • Nightly build/test cycle. • C and F77 APIs are provided. • Seeking feedback and test cases from CF users.

  8. Other Software Efforts • Climate Model Output Rewritter (CMOR). • CFIO from NASA/GMAO. • Brian Ermold (ACRF Development) DOD project (just discovered).

  9. Libcf and NetCDF-4

  10. nccf_def_convention nccf_inq_convention nccf_def_file nccf_add_history File Level Functions • Mark file as CF-1.0 • Does file follow CF-1.0 • Write or read CF recommended global attributes (title, history, institution, source, etc.)‏

  11. nccf_def_var nc_inq_var nccf_def_var_missing nc_inq_var_missing nccf_def_notes nccf_inq_notes Variable Functions • Define or read CF recommended variable attributes (units, fill_value, institution, etc.)‏

  12. nc_def_latitude nc_inq_latitude nc_def_longitude nc_inq_longitude Lat/Lon Functions • Write and read simple latitude and longitude coordinate variables. • Currently handles simple situations only.

  13. int nccf_def_lvl(int ncid, const char *name, size_t len, nc_type xtype, const char *units, int positive_up, const char *standard_name, const char *formula_terms, int cdm_axis_type, int *lvl_dimidp, int *lvl_varidp); int nccf_inq_lvl(int ncid, char *name, size_t *lenp, nc_type *xtypep, size_t *ft_lenp, char *formula_terms, int *positive_upp, int *lvl_dimidp, int *lvl_varidp); Vertical Dimensions, First Try • A vertical coordinate API, done like the lat/long API, proves more complex.

  14. nccf_def_lvl_sigma/nccf_def_ft_sigma nccf_inq_sigma Similarly for atmosphere_ln_pressure_coordinate, atmosphere_hybrid_height_coordinate, atmosphere_sleve_coordinate, etc. Vertical Dimensions, Second Try • Functions to handle the vertical coordinates in appendix D of the CF 1.0 document. • NetCDF define mode considerations make the situation more complex.

  15. nc_def_time nc_inq_time Time Dimension • Write and read time coordinate variable information.

  16. int nccf_get_vara(int ncid, int varid, float *lat_range, int *nlat, float *lon_range, int *nlon, int lvl_index, int timestep, void *data); Geographic Subsetting • Recent addition to libcf. • Does not yet handle complex cases.

  17. An Example if (nc_create(FILE_NAME_SIMPLE_SIGMA, 0, &ncid)) ERR; if (nccf_def_file(ncid, TITLE, HISTORY)) ERR; /* Create coordinates. */ if (nccf_def_latitude(ncid, NLATS, NC_INT, &lat_did, &lat_vid)) ERR; if (nccf_def_longitude(ncid, NLONS, NC_INT, &lon_did, &lon_vid)) ERR; if (nccf_def_lvl_sigma(ncid, "sigma", NC_FLOAT, NLVLS, &lvl_did, &lvl_vid)) ERR; if (nccf_def_time(ncid, "time", NC_UNLIMITED, NC_FLOAT, TIME_UNITS, "time", &time_did, &time_vid)) ERR; <snip> /* Save the ps and ptop info in formula terms attribute. */ if (nccf_def_ft_sigma(ncid, lvl_vid, ps_vid, ptop_vid)) ERR;

  18. Website and Documentation

  19. Daily Snapshots and Testing

  20. Future of libcf • Better geographic subsetting. • More testing on more sample files. • Continued integration and borrowing of functionality from other CF efforts. • More convenience functions. • Optional standard name table checking. • Optional UDUNITS checking. • CF Conventions 2.0 and beyond. • F90 and C++ APIs.

  21. How to Contribute • Send CF example data files to ed@unidata.ucar.edu • Download and try the libcf library. • Let us know of any additional parallel efforts.

  22. Annual NetCDF Bike Rides • Celebrate your favorite data format with a bike ride! • Wednesday afternoon, rain or shine. • Route to be determined – bike paths if possible!

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