MATLAB Programming

Hierarchical Data Format (HDF4) Files
Once you create a data set, you cannot change its name, data type, or
dimensions.
For example, to create a data set in which you can write the following
MATLAB 3-by-5 array of doubles,
A = [ 1 2 3 4 5 ; 6 7 8 9 10 ; 11 12 13 14 15 ];
you could call hdfsd, specifying as arguments 'create' andavalidHDF
file identifier, sd_id. In addition, set the values of the other arguments as
in this code fragment:
ds_name = 'A';
ds_type = 'double';
ds_rank = ndims(A);
ds_dims = fliplr(size(A));
sds_id = hdfsd('create',sd_id,ds_name,ds_type,ds_rank,ds_dims);
If SDcreate can successfully create the data set, it returns an HDF4 SD data
set identifier, (sds_id). Otherwise, SDcreate returns -1.
In this example, note the following:
• The data type you specify in ds_type must match the data type of the
MATLAB array that you want to write to the data set. In the example, the
array is of class double so the value of ds_type is set to 'double'. Ifyou
wanted to use another data type, such as uint8, converttheMATLAB
array to use this data type,
A = uint8([ 1 2 3 4 5 ; 6 7 8 9 10 ; 11 12 13 14 15 ]);
and specify the name of the MATLAB data type, uint8 in this case, in the
ds_type argument.
ds_type = 'uint8';
• The code fragment reverses the order of the values in the dimensions
argument (ds_dims). This processing is necessary because the MATLAB
size function returns the dimensions in column-major order and HDF4
expects to receive dimensions in row-major order.
7-65