Re: netCDF files

Scheller, Robert M. wrote:

> Dear John Caron:
>
> I am a grad student at UW-Madison and I have been attempting
> to work with a suite of VEMAP climate data files in the
> netCDF format.  Although the User's Manual for NetCDF Java
> has been helpful, I am utterly stuck.  It appears fairly
> simple to create the NetcdFile class.  However, I want only
> a very small subsection of the data.  It appears that ma2.Index
> would provide this function but I haven't been able to
> make the logical leap from creating the NetcdFile class to
> creating a MultiArray that I can index on.  Specifically, it
> isn't clear to me how to use the MultiArray read() functions
> on a netcdfile.  

Hi Rob: you dont directly manipulate Index, the read() is done on the 
Variable to get an in-memory Array, see example below.

Also, what is the constructor for the Range
> class?  Thanks very much for any information, advise or
> references you could provide.  

see http://www.unidata.ucar.edu/packages/netcdf-java/ and print out the 
"user documentation".
there's also online javadoc there, you can look up the Range class


Sincerely,
> Rob Scheller
>
> Robert M. Scheller
> Dept. Forest Ecology & Management
> University of Wisconsin - Madison
> 1630 Linden Dr., Madison, WI 53706
> w: 608.265.6321
>
> Visit my webpage! http://landscape.forest.wisc.edu/staff/rob/
> Forest Landscape Ecology Lab  http://landscape.forest.wisc.edu


Here's an example that 1) reads a 2x2 subset of an array and then 2) 
reads the entire array and subsets it.


package test.nc2;

import ucar.ma2.*;
import ucar.nc2.*;

import java.io.*;

public class ExampleRead  {

  public static void main(String [] args) {
    new ExampleRead();
  }

  public ExampleRead() {

    try {
      NetcdfFile ncfile = new 
NetcdfFile("E:/metapps/src/test/nc2/mydata.nc");
      System.out.println( "ncfile "+ ncfile);

      Variable temp = ncfile.findVariable("temperature");
      System.out.println( "temperature "+ temp);

      // read subset
      int[] origin = {1,3};// start at index [1,3]
      int[] shape = {2,2}; // 2x2 array

      Array As = temp.read( origin, shape);
      System.out.println( "physical subset");
      printArray( As);

      // read all the data and logically subset it
      Array A = temp.read();
      Range[] r = new Range[2];
      r[0] = new Range(1,2);
      r[1] = new Range(3,4);

      Array Ap = A.section( r); // logical subset
      System.out.println( "logical subset");
      printArray( Ap);


    } catch (InvalidRangeException e) {
      System.err.println("ERROR reading file "+e);
      return;
    } catch (IOException e) {
      System.err.println("ERROR reading file "+e);
      return;
    }

  }

  private void printArray( Array a) {
    IndexIterator iter = a.getIndexIterator();
    while (iter.hasNext())
      System.out.println( iter.getDoubleNext()+ ",");
  }
}