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.
