Re: skip, stride reading...

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:

 /**
  * 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

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

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.