Supporting HDF5 in GrADS Jennifer M. Adams and Brian E. Doty IGES/COLA

What is GrADS?  GrADS is an interactive desktop tool used for easy access, analysis, and visualization of earth science data.  Two data models: gridded and in situ  Handles many data formats: binary, GRIB, BUFR, netCDF, and HDF4  OPeNDAP-enabled client and server (GDS)

Outline  GrADS Development  The Ensemble Dimension  GrADS and HDF

GrADS Development  Fifth ensemble dimension  New interfaces for GRIB2 and HDF5  Internal data handling in double precision  Mask for missing data  Graphics improvements  New output options for GIS applications  Third data model: Quasi-regular grids

Ensemble Handling  A true 5th dimension for ensemble members ‘set X, Y, Z, T, or E’  A virtual dimension for forecast time offset ‘display sst(ft=2)’ ‘display sst(ftime=24hr)’

GrADS Metadata Requirements for Ensemble Members  Unique name / number  Initial time  Length  One time axis must span all members  All members must share common grid

The GrADS-GDS Coupled System  The GDS serves any GrADS data set  GrADS is a client for all GDS data sets  The NetCDFification of the ensemble metadata must be meaningful to GrADS  Emerging metadata standard for ensembles

Ensembles: Same Length, Same Initial Time Time Axis ----> Ensemble Member

Ensembles: Same Length, Different Initial Times Time Axis ----> Ensemble Member

Ensembles: Same Length, Different Initial Times Time Axis ----> Ensemble Member

Ensembles: Same Length, Different Initial Times Time Axis ----> Ensemble Member

Ensembles: Same Length, Different Initial Times Time Axis ----> Ensemble Member

NCEP CFS: Different Lengths, Different Initial Times Time Axis ----> Ensemble Member

“ new = variable (ft=2) ” Time Axis ----> Ensemble Member

“ new = ftloop (variable, ftime=12hr, ftime=48hr) ” Time Axis ----> Ensemble Member

GrADS and HDF: A Brief History  GrADS reads HDF4 and NC files Metadata must be COARDS-compliant Uses NC v2 API  GrADS writes HDF4 and NC files Uses LATS interface and NC v2 API  GrADS becomes a DODS client NC v3 API is added  New interface for non-compliant HDF4 and NC files External metadata is user-provided Uses SD and NC APIs

GrADS 1.9 Executables NetCDFHDF4DODSLibraries gradsc ---Core libs gradshdf ReadRead/Write-Core libs + libdf + libmfhdf gradsnc Read/Write--Core libs + libnetcdf gradsdods Read/Write-ReadCore libs + libnc-dap Core libs: X11, readline, zlib, png, gd Extra dependent libs: udunits, jpeg, szip, xml2, curl, dap, gadap

GrADS and HDF: Current Events  GrADS (now GPL) must drop (copyrighted) LATS  New interfaces to be written for NC and HDF output  HDF4 handling isolated using SD API exclusively  NC handling reworked using v3 API, ready for v4

GrADS 2.0 Executables NetCDFHDF4OPeNDAPLibraries grads Read (Write TBA) - Core libs + libdf + libmfhdf + libnetcdf gradsdap Read (Write TBA) Read Core libs + libdf + libmfhdf + libnc-dap Core libs: X11, readline, zlib, png, gd, jpeg, jasper, grib2c Extra dependent libs: udunits, szip, xml2, curl, dap, gadap

GrADS and HDF5: The Future  First Option: Link with NetCDF-4 library Very easy Only supports HDF5 created with NetCDF-4 Destined to repeat HDF4 history?  Second Option: Link with HDF5 library Requires a new HDF5 interface More general support of HDF5 Keeps NetCDF interface independent Necessary for quasi-regular swath data?