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GeoTrellis is an open source geographic data processing engine for high performance applications.
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package org.osgeo.proj4j;

import org.osgeo.proj4j.datum.Datum;
import org.osgeo.proj4j.datum.Ellipsoid;
import org.osgeo.proj4j.proj.LongLatProjection;
import org.osgeo.proj4j.proj.Projection;
import org.osgeo.proj4j.units.Unit;
import org.osgeo.proj4j.units.Units;

/**
 * Represents a projected or geodetic geospatial coordinate system,
 * to which coordinates may be referenced.
 * A coordinate system is defined by the following things:
 * 
 * an {@link Ellipsoid} specifies how the shape of the Earth is approximated
 * 
a {@link Datum} provides the mapping from the ellipsoid to
 * actual locations on the earth
 * 
a {@link Projection} method maps the ellpsoidal surface to a planar space.
 * (The projection method may be null in the case of geodetic coordinate systems).
 * 
a {@link Unit} indicates how the ordinate values
 * of coordinates are interpreted
 * 
 *
 * @author Martin Davis
 *
 * @see CRSFactory
 *
 */
// CoordinateReferenceSystem corresponds to the PJ struct from proj.4
public class CoordinateReferenceSystem implements java.io.Serializable
{
    // allows specifying transformations which convert to/from Geographic coordinates on the same datum
    public static final CoordinateReferenceSystem CS_GEO = new CoordinateReferenceSystem("CS_GEO", null, null, null);

    //TODO: add metadata like authority, id, name, parameter string, datum, ellipsoid, datum shift parameters

    private String name;
    private String[] params;
    private Datum datum;
    private Projection proj;

    public CoordinateReferenceSystem(String name, String[] params, Datum datum, Projection proj)
    {
        this.name = name;
        this.params = params;
        this.datum = datum;
        this.proj = proj;

        if (name == null) {
            String projName = "null-proj";
            if (proj != null)
                projName = proj.getName();
            this.name = projName + "-CS";
        }
    }

    public String getName()
    {
        return name;
    }

    public String[] getParameters()
    {
        return params;
    }

    public Datum getDatum()
    {
        return datum;
    }

    public Projection getProjection()
    {
        return proj;
    }

    public String getParameterString()
    {
        if (params == null) return "";

        StringBuffer buf = new StringBuffer();
        for (int i = 0; i < params.length; i++) {
            buf.append(params[i]);
            buf.append(" ");
        }
        return buf.toString();
    }

    public Boolean isGeographic()
    {
        return proj.isGeographic();
    }

    /**
     * Creates a geographic (unprojected) {@link CoordinateReferenceSystem}
     * based on the {@link Datum} of this CRS.
     * This is useful for defining {@link CoordinateTransform}s
     * to and from geographic coordinate systems,
     * where no datum transformation is required.
     * The {@link Units} of the geographic CRS are set to {@link Units#DEGREES}.
     *
     * @return a geographic CoordinateReferenceSystem based on the datum of this CRS
     */
    public CoordinateReferenceSystem createGeographic()
    {
        Datum datum = getDatum();
        Projection geoProj = new LongLatProjection();
        geoProj.setEllipsoid(getProjection().getEllipsoid());
        geoProj.setUnits(Units.DEGREES);
        geoProj.initialize();
        return new CoordinateReferenceSystem("GEO-" + datum.getCode(), null, datum, geoProj);
    }

    public String toString() { return name; }
}