GeoAPI

• Type: Sub-task
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.1-M4
• Fix Version/s: 2.1
• Component/s: geometry
• Labels:

  None

Sanjay requested a createPosition( Position ) method for GeometryFactory ... and it took me a little while to see the utility. The preceeding technique was to treat DirectPosition as a data object and call clone().

This was in error:

• DirectPosition is not defined as a data object at this time (equals and hashcode are not defined)
• DirectPosition should not be exactly copied in the case where it is a wrapper (ie Point or List<DirectPosition backed by a double array)

Proposed changed:

/**
     * Makes an exact copy of this coordinate.
     * @deprecated Please use PositionFactory.createPosition( position )
     */
    /*{DirectPosition}*/ Object clone();

DirectPosition is however actually used in the wild - and I need to
explain what the consequences are of using clone the way it is provided.
If you
consider DirectPosition a "data object" you would expect clone() to
give you a copy that you could proceed to manipulate on your own as
needed.

When working on List<DirectPosition> backed by a double array the
instances you get back are actually thin wrappers instead. Performing a
clone on one
of these will not give you the isolation you crave.

Having a List<DirectPosition> built over top of a double array is a very
important story from a performance stand point ... worth killing clone over.

Here is a sample (untested implementation) for discussion purposes:

public List<DirectPosition> createPositionList( final double[] array, final int start, final int end ) {        
        return new AbstractList<DirectPosition>(){
            @Override
            public DirectPosition get( final int index ) {
                return new DirectPosition(){
                    int position = start + ( crs.getCoordinateSystem().getDimension() * index );
                    
                    public CoordinateReferenceSystem getCoordinateReferenceSystem() {
                        return crs;
                    }
                    public double[] getCoordinates() {
                        double coords[] = new double[ crs.getCoordinateSystem().getDimension() ];
                        System.arraycopy(array, position, coords, 0, crs.getCoordinateSystem().getDimension() );                        
                        return coords;
                    }

                    public int getDimension() {
                        return crs.getCoordinateSystem().getDimension();
                    }

                    public double getOrdinate( int dimension ) throws IndexOutOfBoundsException {
                        return array[position+dimension];
                    }

                    public void setOrdinate( int dimension, double value ) throws IndexOutOfBoundsException {
                        array[position+dimension] = value;                        
                    }

                    public DirectPosition getPosition() {
                        return this;
                    }
                    @Override
                    public Object clone() {
                        try {
                            return super.clone();
                        } catch (CloneNotSupportedException e) {
                            return null; // ignore?                            
                        }                        
                    }
                };
            }
            public int size() {
                return end-start / crs.getCoordinateSystem().getDimension();
            }
        };
    }

I would like to confirm my understanding is correct before tormenting
GeoTools with a new SNAPSHOT.

• Assignee:

  Martin Desruisseaux

  Reporter:

  Jody Garnett

• Created:

  20/Mar/07 7:42 PM

  Updated:

  02/Jun/09 11:22 AM

  Resolved:

  28/Nov/07 5:49 AM