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NOTICE: This version of the NSF Unidata web site (archive.unidata.ucar.edu) is no longer being updated.
Current content can be found at unidata.ucar.edu.
To learn about what's going on, see About the Archive Site.
On Jul 13, 2016, at 6:04 PM, Roy Mendelssohn - NOAA Federal <roy.mendelssohn@xxxxxxxx<mailto:roy.mendelssohn@xxxxxxxx>> wrote: Since Aleksander has kindly answered my first question, this raises a second question on HDF virtual files - is each file in the virtual file a "valid" file in and of itself, that is combined by whoever is the "base" file of the virtual file, or does it depend on the "base" file. Let’s first inter-calibrate the HDF and netCDF vocabularies to avoid confusion: * HDF5 dataset = netCDF variable * HDF5 file = netCDF dataset. About HDF5 virtual datasets: * There are no HDF5 virtual files, only HDF5 virtual datasets inside a normal HDF5 file. * The data for a HDF5 virtual dataset comes from source HDF5 datasets located in other HDF5 files. * HDF5 virtual datasets can have “local” data in addition to the data coming from source datasets. * Every HDF5 file with virtual datasets is a valid HDF5 file. Source datasets are just ordinary HDF5 datasets so files with them are valid HDF5 files, too. * How the data from a source dataset is presented in its virtual dataset is controlled by a mapping between the two dataset's HDF5 dataspaces (start, stride, count, block). * These mappings are set on HDF5 dataset creation and cannot be changed. * There are HDF5 dataset access property settings that define how to deal with missing source dataset data. (See my previous email.) These can be changed each time a virtual dataset is opened for access. * The fill value is used for any missing data in a virtual dataset. User’s guide for the virtual dataset feature is being prepared; in the meantime: https://www.hdfgroup.org/HDF5/Tutor/vds.html. -Aleksandar
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