Re: skip, stride reading...

• To: Tom Rink <rink@xxxxxxxxxxxxx>, support-netcdf-java@xxxxxxxxxxxxxxxx
• Subject: Re: skip, stride reading...
• From: John Caron <caron@xxxxxxxxxxxxxxxx>
• Date: Fri, 17 Oct 2003 16:51:49 -0600

Tom Rink wrote:

Hi John,

John Caron wrote:

Tom Rink wrote:

Hi,

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

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 = var.read();
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,

Tom

ah! a DODS file. thats much easier.

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

 /**

  * <p>

  * <p>
  * @param origin int array specifying the starting index.

  * @param stride  int array specifying the stride in each dimension.
  * @return the requested data in a memory-resident Array
  */

its in

ftp://ftp.unidata.ucar.edu/pub/netcdf-java/v2.1/netcdfAll-05.jar

• References:
  • Re: skip, stride reading...
    • From: John Caron