MATLAB Programming

7 Working with Scientific Data Formats
Step 3: Writing MATLAB Data to an HDF4 File. After creating an
HDF4 file and creating a data set in the file, you can write data to the entire
data set or just a portion of the data set. In the HDF4 SD API, you use the
SDwritedata routine. In MATLAB, use the hdfsd function, specifying as
arguments:
• Name of the SD API routine, 'writedata' in this case
• ValidHDF4SDdatasetidentifier,sds_id, returned by SDcreate
• Location in the data set where you want to start writing data, called the
start vector in HDF4 terminology
• Number of elements along each dimension to skip between each write
operation, called the stride vector in HDF4 terminology
• Total number of elements to write along each dimension, called the edges
vector in HDF4 terminology
• MATLAB array to be written
Note You must specify the values of the start, stride, and edges arguments
in row-major order, rather than the column-major order used in MATLAB.
Note how the example uses fliplr to reverse the order of the dimensions in
the vector returned by the size function before assigning it as the value of
the edges argument.
The values you assign to these arguments depend on the MATLAB array
you want to export. For example, the following code fragment writes this
MATLAB 3-by-5 array of doubles,
A = [ 1 2 3 4 5; 6 7 8 9 10; 11 12 13 14 15 ];
into an HDF4 file:
ds_start = zeros(1:ndims(A)); % Start at the beginning
ds_stride = [];
% Write every element.
ds_edges = fliplr(size(A)); % Reverse the dimensions.
stat = hdfsd('writedata',sds_id,...
ds_start, ds_stride, ds_edges, A);
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