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/*
Copyright 2011 Martin Davis

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/package org.osgeo.proj4j.proj;

import org.osgeo.proj4j.*;

public class Eckert6Projection extends PseudoCylindricalProjection {

    private static final double n = 2.570796326794896619231321691;
    private static final double C_y = Math.sqrt((2) / n);
    private static final double C_x = C_y / 2;
    private static final int MAX_ITER = 8;
    private static final double LOOP_TOL = 1e-7;

    public ProjCoordinate project(double lam, double phi, ProjCoordinate xy) {

        int i;
        double k, V;
        k = n * Math.sin(phi);
        for (i = MAX_ITER; i > 0;) {
            phi -= V = (phi + Math.sin(phi) - k) / (1 + Math.cos(phi));
            if (Math.abs(V) < LOOP_TOL) {
                break;
            }
            --i;
        }
        if (i == 0) {
            throw new ProjectionException("F_ERROR");
        }

        xy.x = C_x * lam * (1 + Math.cos(phi));
        xy.y = C_y * phi;
        return xy;
    }

    public ProjCoordinate projectInverse(double x, double y, ProjCoordinate lp) {
        y /= C_y;
        lp.y = Math.asin((y + Math.sin(y)) / n);
        lp.x = x / (C_x * (1 + Math.cos(y)));
        return lp;
    }

    public boolean hasInverse() {
        return true;
    }

    public boolean isEqualArea() {
        return true;
    }

    public String toString() {
        return "Eckert VI";
    }
}