MATLAB Programming

7 Working with Scientific Data Formats
Note The following sections, when referring to specific routines in the HDF4
SD API, use the C library name rather than the MATLAB function name. The
MATLAB syntax is used in all examples.
Step 1: Opening the HDF4 File. To import an HDF4 SD data set, you must
first open the file using the SD API routine SDstart. (InHDF4terminology,
the numeric arrays stored in HDF4 files are called data sets.) In MATLAB,
you use the hdfsd function, specifying as arguments:
• Name of the SD API routine, start in this case.
• Name of the file you want to open.
• Mode in which you want to open it. The following table lists the file access
modes supported by the SDstart routine. In MATLAB, you specify these
modesastextstrings.YoucanspecifythefullHDF4modenameoroneof
the abbreviated forms listed in the table.
HDF4 File Creation
Mode HDF4 Mode Name MATLAB String
Create a new file 'DFACC_CREATE' 'create'
Read access 'DFACC_RDONLY' 'read' or 'rdonly'
Read and write access 'DFACC_RDWR' 'rdwr' or 'write'
For example, this code opens the file mydata.hdf for read access:
sd_id = hdfsd('start','mydata.hdf','read');
If SDstart can find and open the file specified, it returns an HDF4 SD file
identifier, named sd_id in the example. Otherwise, it returns -1.
Step 2: Retrieving Information About the HDF4 File. To get information
about an HDF4 file, you must use the SD API routine SDfileinfo. This
function returns the number of data sets in the file and the number of global
attributes in the file, if any. (For more information about global attributes, see
“Example: Exporting Data Using the HDF4 SD API Functions” on page 7-63.)
In MATLAB, you use the hdfsd function, specifying the following arguments:
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