The Hierarchical Data Format
(HDF5) is a open-source, cross-platform,
data storage solution originally developed at the National Center for Supercomputing Applications (NCSA) for storage of scientific data
and descriptive meta-data in an organised heirarchy. This project extends the power of HDF5 to LabVIEW,
which is potentially very useful
in many applications.
This project provides HDF5 v1.8.14
(released November 2014) functionality
to LabVIEW 2010 or newer
, and is available
as a self-installing package (*.vip file), installable through the VI Package Manager
or directly from the repository
News alert: h5labview
can be used to read/write MAT files to share data with MATLAB, check out
the new example
to see how!
To demonstrate how easy it is to use h5labview
, here's an example showing creation of a new HDF5 file and writing
a dataset with an attribute inside a nested group. A screenshot from HDFView showing the hierarchy of the generated file
and the dataset is shown to the right.
As of version 2, h5labview
supports compound datatypes (clusters) with "table" access, as demonstrated below.
The table below lists the datatypes supported by h5labview
in version 2, and their state of implementation.
See this FAQ entry
on why not all types are planned to be supported.
|LabVIEW type||HDF type||Notes
|I8..I64||H5T_NATIVE_INT8 .. H5T_NATIVE_INT64||Native-endian numerical formats|
|U8..U64||H5T_NATIVE_UINT8 .. H5T_NATIVE_UINT64|
|SGL, DBL||H5T_NATIVE_FLOAT, H5T_NATIVE_DOUBLE|
|CSG, CDB||H5T_COMPOUND||Compound with "real" and "imag" components|
|EXT, CEX||Custom H5T_FLOAT||Host-compatible extended precision type1|
|Physical quantities||Committed H5T_FLOAT||Written in SI units as named compounds|
|U8..U64||H5T_BITFIELD||Read-only support for BITFIELD datatypes as unsigned integers|
|String||H5T_STRING||Both variable and fixed strings2|
|Boolean||H5T_ENUM||Enumeration of "false"=0 and "true"=1|
|Clusters||H5T_COMPOUND||Valid clusters may contain any of the above types|
|Arrays||Implemented as dataspaces3||Array can be of any dimension of above type, including clusters|
|Enums||H5T_ENUM||LabVIEW enums supported4|
|Images||As per specification||Writing of Grayscale, Truecolor and Palette images supported|
|Waveforms||Datasets of relevant type with attributes||In development|
- LabVIEW's memory layout for EXT varies across platforms, as does HDF's extended H5T_NATIVE_LDOUBLE.
A custom HDF type is created corresponding to the EXT layout on the host machine and HDF performs conversions automatically.
This should lead to no precision loss when writing, and enables reading at the greatest precision of the host.
The procedure is detailed in this FAQ entry.
- HDF supports two types of strings: fixed and variable length. Variable-length strings are implemented and used by default, but LabVIEW
strings that contain the null character (\0) must be written as fixed strings. Whether a string is read/written as fixed or variable
is configured in LabVIEW, as described in this FAQ entry.
- Arrays are implemented in HDF5 with a separate "dataspace" interface. Although an array datatype does exists, the H5T_ARRAY is inefficient
and serves limited purpose. The array datatype therefore will not be implemented, neither will arrays of arrays nor clusters including arrays.
- LabVIEW defines enums as a set of contiguous unsigned integers. HDF5 sets no such restriction, so as such any LabVIEW enum can be written
to an HDF file but HDF5 enums must be read as (signed) integers.