This slide explains how GrADS can access HDF5 files.

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

2. 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)

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

4. 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


5. 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)‟

6. 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


7. 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

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

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

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

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

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

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

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

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

16. 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

17. GrADS 1.9 Executables
NetCDF
HDF4
DODS
-
-
-
Core libs
gradshdf
Read
Read/Writ
e
-
Core libs + libdf +
libmfhdf
gradsnc
Read/Writ
e
-
-
Core libs + libnetcdf
gradsdod
s
Read/Writ
e
-
Read
Core libs + libnc-dap
gradsc
Libraries
Core libs: X11, readline, zlib, png, gd
Extra dependent libs: udunits, jpeg, szip, xml2, curl, dap, gadap

18. 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

19. GrADS 2.0 Executables
NetCDF
Read
(Write TBA)
gradsda
p
OPeNDA
P
Read
grads
HDF4
(Write TBA)
-
Read
Read
(Write TBA)
(Write TBA)
Read
Libraries
Core libs + libdf +
libmfhdf
+ libnetcdf
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

20. 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?