[visad] sampling error bugs

Hi,

I'm trying to use error estimation in VisAD. I'd still prefer to useFlatFields but the implemented error code won't give me an error foreach data value. Instead, I am using a FieldImpl with a range ofRealTuple[]. Internally, there are Real-s that will estimate errors forbinary and unary operations. In the process of doing this, I've runinto a few bugs. I've also proposed a couple of bug fixes.


1) Tuple.adjustSamplingError():

When resampleDouble() calls adjustSamplingError() on my RealTuple, itdelegates to Tuple's adjustSamplingError() which creates a new Tuple.But since the range type is RealTupleType, the Tuple constructorrequires that a RealTuple be constructed instead of a Tuple. I fixedthis by overriding adjustSamplingError() in RealTuple:

  public Data adjustSamplingError(Data error, int error_mode)
         throws VisADException, RemoteException {
      if (isMissing() || error == null || error.isMissing()) return this;
      int n = getDimension();
      Real[] newComponents = new Real[n];
      for (int i=0; i<n; i++) {
          Real errorComponent = (Real) ((RealTuple) error).getComponent(i);
          newComponents[i] = (Real)
              getComponent(i).adjustSamplingError(errorComponent, error_mode);
      }

return new RealTuple(newComponents);}


2) Real.adjustSamplingError()

When calling adjustSamplingError() on a Real with no (i.e. null)ErrorEstimate, the method returns itself (with no error) instead ofadding the contribution of the "error" argument. I modified the routineto use an error of 0 if the ErrorEstimate is null:

  public Data adjustSamplingError(Data error, int error_mode)
  throws VisADException, RemoteException {
      if (isMissing() || error == null || error.isMissing()) return this;
      int n = getDimension();
      Real[] newComponents = new Real[n];
      for (int i=0; i<n; i++) { >   public Data adjustSamplingError(Data error, 
int error_mode)
         throws VisADException, RemoteException {
    if (isMissing() || error == null || error.isMissing()) return this;
    double a = ((Real) error).getValue();
    double b = (Error == null) ? 0 : Error.getErrorValue();
    double e = (error_mode == INDEPENDENT) ? Math.sqrt(a * a + b * b) :
                                             Math.abs(a) + Math.abs(b);
    return new Real((RealType) Type, Value, unit,
                    new ErrorEstimate(Value, e, unit));
  }


3) FieldImpl.resampleDouble()

When estimating errors with WEIGHTED_AVERAGE sampling, the variable"coefs" is redefined as a new double array within a loop (near line3272). It is not initialized but the code tries to access it in the nextloop iteration with unhappy results. I didn't try to follow the logic tomake a fix.

So, is it worth going down this path? It appears that the errorestimation is not fully implemented, not to mention that theErrorEstimate comments for unary and binary operation error estimatessay that they are, "actually, more of a WAG than an estimate. Theseformulas are a bit of a hack and suggestions for improvements arewelcome." As I've mentioned before, I'd like to see FlatField keep anerror estimate for each range value and propagate them through the mathand resampling operations. I figured if Real-s can do it, why notFlatFields. Is anyone using visad ErrorEstimate-s or have any thoughtson doing this?


Thanks,
Doug