Transcript Demonstration of New Capabilities in GrADS

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
Ensemble Member
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 ---->
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
NetCDF
HDF4
DODS
-
-
-
Core libs
gradshdf
Read
Read/Write
-
Core libs + libdf + libmfhdf
gradsnc
Read/Write
-
-
Core libs + libnetcdf
gradsdods
Read/Write
-
Read
Core libs + libnc-dap
gradsc
Libraries
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
grads
gradsdap
NetCDF
HDF4
OPeNDAP
Libraries
Read
Read
(Write TBA)
(Write TBA)
-
Core libs + libdf + libmfhdf
+ libnetcdf
Read
Read
(Write TBA)
(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?