/**
 * echarts地图投射算法
 *
 * @desc echarts基于Canvas，纯Javascript图表库，提供直观，生动，可交互，可个性化定制的数据统计图表。
 * @author Kener (@Kener-林峰, kener.linfeng@gmail.com)
 *
 */
define(function() {
    // 墨卡托投射
    function _mercator() {
        var radians = Math.PI / 180;
        var scale = 500;
        var translate = [480, 250];

        function mercator(coordinates) {
            var x = coordinates[0] / 360;
            var y = -(Math.log(Math.tan(
                        Math.PI / 4 + coordinates[1] * radians / 2
                    )) / radians) / 360;
            return [
                scale * x + translate[0],
                scale * Math.max(-0.5, Math.min(0.5, y)) + translate[1]
            ];
        }


        mercator.invert = function (coordinates) {
            var x = (coordinates[0] - translate[0]) / scale;
            var y = (coordinates[1] - translate[1]) / scale;
            return [
                360 * x,
                2 * Math.atan(Math.exp(-360 * y * radians)) / radians - 90
            ];
        };

        mercator.scale = function (x) {
            if (!arguments.length) {
                return scale;
            }
            scale = +x;
            return mercator;
        };

        mercator.translate = function (x) {
            if (!arguments.length) {
                return translate;
            }
            translate = [+x[0], +x[1]];
            return mercator;
        };

        return mercator;
    }

    return _mercator;
});