/**
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* echarts地图投射算法
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*
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* @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。
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* @author Kener (@Kener-林峰, kener.linfeng@gmail.com)
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*
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*/
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define(function() {
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// Derived from Tom Carden's Albers implementation for Protovis.
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// http://gist.github.com/476238
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// http://mathworld.wolfram.com/AlbersEqual-AreaConicProjection.html
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function _albers() {
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var radians = Math.PI / 180;
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var origin = [0, 0]; //[-98, 38],
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var parallels = [29.5, 45.5];
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var scale = 1000;
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var translate = [0, 0]; //[480, 250],
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var lng0; // radians * origin[0]
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var n;
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var C;
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var p0;
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function albers(coordinates) {
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var t = n * (radians * coordinates[0] - lng0);
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var p = Math.sqrt(
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C - 2 * n * Math.sin(radians * coordinates[1])
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) / n;
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return [
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scale * p * Math.sin(t) + translate[0],
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scale * (p * Math.cos(t) - p0) + translate[1]
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];
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}
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albers.invert = function (coordinates) {
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var x = (coordinates[0] - translate[0]) / scale;
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var y = (coordinates[1] - translate[1]) / scale;
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var p0y = p0 + y;
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var t = Math.atan2(x, p0y);
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var p = Math.sqrt(x * x + p0y * p0y);
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return [
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(lng0 + t / n) / radians,
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Math.asin((C - p * p * n * n) / (2 * n)) / radians
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];
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};
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function reload() {
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var phi1 = radians * parallels[0];
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var phi2 = radians * parallels[1];
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var lat0 = radians * origin[1];
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var s = Math.sin(phi1);
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var c = Math.cos(phi1);
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lng0 = radians * origin[0];
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n = 0.5 * (s + Math.sin(phi2));
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C = c * c + 2 * n * s;
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p0 = Math.sqrt(C - 2 * n * Math.sin(lat0)) / n;
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return albers;
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}
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albers.origin = function (x) {
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if (!arguments.length) {
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return origin;
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}
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origin = [+x[0], +x[1]];
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return reload();
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};
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albers.parallels = function (x) {
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if (!arguments.length) {
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return parallels;
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}
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parallels = [+x[0], +x[1]];
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return reload();
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};
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albers.scale = function (x) {
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if (!arguments.length) {
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return scale;
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}
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scale = +x;
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return albers;
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};
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albers.translate = function (x) {
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if (!arguments.length) {
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return translate;
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}
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translate = [+x[0], +x[1]];
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return albers;
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};
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return reload();
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}
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return _albers;
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});
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