How about the following interface? The ordinates array has the same
semantics as ordinates in a JTS CoordinateSequence. The values in the
ordinates array are modified in place by the CoordinateOperation.
public interface CoordinateOperation {
void perform(double[] ordinates);
}
For projections you may have an interface such as the following as a
convenience to get both the forward and inverse operations.
public interface Projection {
CoordinateOperation getOperation();
CoordinateOperation getInverseOperation();
}
A chained operation may look like the following.
public class ChainedOperation implements CoordinateOperation {
private CoordinateOperation[] operations;
public void perform(double[] ordinates) {
for (CoordinateOperation operation : operations) {
operation.perform(ordinates;
}
}
}
Paul
Paul Austin wrote:
> I've come up with a very simple interface for projection algorithms. The
> purpose of this is to be model neutral (not tied to JTS), as such it is
> not for use by end users but instead for use in higher level libraries
> that would work on JTS geometries.
>
> public interface Projection {
> void forward();
>
> void reverse();
>
> double getX();
> void setX(double x);
>
> double getY();
> void setY(double y);
>
> }
>
>
> To perform a forward projection the code would be as follows.
>
> projection.setX(lonDegrees);
> projection.setY(latDegrees);
> projection.forward();
> x = projection.getX();
> y = projection.getY();
>
>
>
> Reverse projection would be similar.
>
> projection.setX(xMetres);
> projection.setY(yMetres);
> projection.reverse();
> lonDegrees = projection.getX();
> latDegrees = projection.getY();
>
> NOTE: The interface is not thread safe.
>
> The design goals were it must be simple and not require any temporary
> objects.
>
> A JTS wrapper for this would have the following two basic methods
>
>
> public Coordinate forward(double x, double y, double z) {
> projection.setX(x);
> projection.setY(y);
> projection.forward();
> Coordinate coordinate = new Coordinate(projection.getX(),
> projection.getY(),z);
> forwardPrecisionModel.makePrecise(coordinate);
> return coordinate;
> }
>
> public Coordinate reverse(double x, double y, double z) {
> projection.setX(x);
> projection.setY(y);
> projection.reverse();
> Coordinate coordinate = new Coordinate(projection.getX(),
> projection.getY(),z);
> reversePrecisionModel.makePrecise(coordinate);
> return coordinate;
> }
>
> plus a number of other methods to deal with all the JTS Geometry types,
> see attached for full implementation. Note that there could be a
> performance optimization for coordinate sequences to directly deal with
> the Projection interface.
>
> Most projections go to/from Geographics to a Cartesian system to go from
> one Cartesian to another Cartesian you would need a chained projection
> which goes from one to another.
>
> The last piece in the puzzle is to have a ProjectionFactory that can
> create projections from EPSG srid codes. There can be many factory
> implementations, e.g. one to wrap FME, one to wrap the Java Projection
> Library, one for JUMP specific projections and one for GeoTools. You
> would then interact with an instance of the factory to create your
> projections and then use either the Projection interface or the
> JtsProjection wrapper.
>
> What do you guys think?
>
> Paul
>
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