Re: skip, stride reading...

Tom Rink wrote:

Hi John,

John Caron wrote:

Tom Rink wrote:


How can skip or stride reading be done in the Java
implementation of NetCDF? Is there an equivalent

Tom Rink

Hi Tom:

I seem to have overlooked implementing a stride-based read, probably because the original (version 1) library doesnt have one. I will add this to the to-do list.

Meanwhile, you can get a strided subset of an Array, which will be equivilent except that you probably have to read more than you need:

Suppose you have a 3D Array, and you want to access it with stride 2, 1, and 3 in the three dimensions. The following will give you a logical view of the data with those strides, using the same backing data as the original:

Array data =;
int[] shape = data.getShape();
Array dataS;
Range[] ranges = new Range[] { new Range(0,shape[0]-1, 2), null, new Range(0,shape[2]-1, 3) };

try {
dataS = data.section( ranges);
} catch (InvalidRangeException e) {
System.out.println("testStride failed == "+ e);

Thanks for the work-around, but the read() in this case would be much too much: I have MODIS on a remote server that I'm accessing via DODS and I want to produce a low-res image of the entire swath so the user can decide what channels or regions are important,
then subsetting/slicing can be used to focus on the point of interest.

For now, I'll have to sub-sample on the client, Is there any way to know
when the stride capability will be implemened?

Thanks again for you help,


ah! a DODS file. thats much easier.

I just put out an experimental version that has this method in DODSVariable:

* Read data from the DODS dataset with strides, and return a memory resident Array. * This Array has the same element type as the IOArray, and the requested shape.
  * <p>
* <code>assert(origin[ii] + shape[ii]*stride[i] <= Variable.shape[ii]); </code>
  * <p>
  * @param origin int array specifying the starting index.
* @param shape int array specifying the extents in each dimension. This becomes the shape of the returned Array.
  * @param stride  int array specifying the stride in each dimension.
  * @return the requested data in a memory-resident Array
public Array read(int [] origin, int [] shape, int stride[]) throws IOException, InvalidRangeException;

its in

ive tested it a bit, i would appreciate it if youd try it and check the results and let me know if you see any problems.

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