client/components/conveyal/transitive.js/master/lib/util/spherical-mercator.js
var SphericalMercator = (function() {
// Closures including constants and other precalculated values.
var cache = {},
EPSLN = 1.0e-10,
D2R = Math.PI / 180,
R2D = 180 / Math.PI,
// 900913 properties.
A = 6378137,
MAXEXTENT = 20037508.34;
// SphericalMercator constructor: precaches calculations
// for fast tile lookups.
function SphericalMercator(options) {
options = options || {};
this.size = options.size || 256;
if (!cache[this.size]) {
var size = this.size;
var c = cache[this.size] = {};
c.Bc = [];
c.Cc = [];
c.zc = [];
c.Ac = [];
for (var d = 0; d < 30; d++) {
c.Bc.push(size / 360);
c.Cc.push(size / (2 * Math.PI));
c.zc.push(size / 2);
c.Ac.push(size);
size *= 2;
}
}
this.Bc = cache[this.size].Bc;
this.Cc = cache[this.size].Cc;
this.zc = cache[this.size].zc;
this.Ac = cache[this.size].Ac;
}
// Convert lon lat to screen pixel value
//
// - `ll` {Array} `[lon, lat]` array of geographic coordinates.
// - `zoom` {Number} zoom level.
SphericalMercator.prototype.px = function(ll, zoom) {
var d = this.zc[zoom];
var f = Math.min(Math.max(Math.sin(D2R * ll[1]), -0.9999), 0.9999);
var x = Math.round(d + ll[0] * this.Bc[zoom]);
var y = Math.round(d + 0.5 * Math.log((1 + f) / (1 - f)) * (-this.Cc[
zoom]));
if (x > this.Ac[zoom]) x = this.Ac[zoom];
if (y > this.Ac[zoom]) y = this.Ac[zoom];
//(x < 0) && (x = 0);
//(y < 0) && (y = 0);
return [x, y];
};
// Convert screen pixel value to lon lat
//
// - `px` {Array} `[x, y]` array of geographic coordinates.
// - `zoom` {Number} zoom level.
SphericalMercator.prototype.ll = function(px, zoom) {
var g = (px[1] - this.zc[zoom]) / (-this.Cc[zoom]);
var lon = (px[0] - this.zc[zoom]) / this.Bc[zoom];
var lat = R2D * (2 * Math.atan(Math.exp(g)) - 0.5 * Math.PI);
return [lon, lat];
};
// Convert tile xyz value to bbox of the form `[w, s, e, n]`
//
// - `x` {Number} x (longitude) number.
// - `y` {Number} y (latitude) number.
// - `zoom` {Number} zoom.
// - `tms_style` {Boolean} whether to compute using tms-style.
// - `srs` {String} projection for resulting bbox (WGS84|900913).
// - `return` {Array} bbox array of values in form `[w, s, e, n]`.
SphericalMercator.prototype.bbox = function(x, y, zoom, tms_style, srs) {
// Convert xyz into bbox with srs WGS84
if (tms_style) {
y = (Math.pow(2, zoom) - 1) - y;
}
// Use +y to make sure it's a number to avoid inadvertent concatenation.
var ll = [x * this.size, (+y + 1) * this.size]; // lower left
// Use +x to make sure it's a number to avoid inadvertent concatenation.
var ur = [(+x + 1) * this.size, y * this.size]; // upper right
var bbox = this.ll(ll, zoom).concat(this.ll(ur, zoom));
// If web mercator requested reproject to 900913.
if (srs === '900913') {
return this.convert(bbox, '900913');
} else {
return bbox;
}
};
// Convert bbox to xyx bounds
//
// - `bbox` {Number} bbox in the form `[w, s, e, n]`.
// - `zoom` {Number} zoom.
// - `tms_style` {Boolean} whether to compute using tms-style.
// - `srs` {String} projection of input bbox (WGS84|900913).
// - `@return` {Object} XYZ bounds containing minX, maxX, minY, maxY properties.
SphericalMercator.prototype.xyz = function(bbox, zoom, tms_style, srs) {
// If web mercator provided reproject to WGS84.
if (srs === '900913') {
bbox = this.convert(bbox, 'WGS84');
}
var ll = [bbox[0], bbox[1]]; // lower left
var ur = [bbox[2], bbox[3]]; // upper right
var px_ll = this.px(ll, zoom);
var px_ur = this.px(ur, zoom);
// Y = 0 for XYZ is the top hence minY uses px_ur[1].
var bounds = {
minX: Math.floor(px_ll[0] / this.size),
minY: Math.floor(px_ur[1] / this.size),
maxX: Math.floor((px_ur[0] - 1) / this.size),
maxY: Math.floor((px_ll[1] - 1) / this.size)
};
if (tms_style) {
var tms = {
minY: (Math.pow(2, zoom) - 1) - bounds.maxY,
maxY: (Math.pow(2, zoom) - 1) - bounds.minY
};
bounds.minY = tms.minY;
bounds.maxY = tms.maxY;
}
return bounds;
};
// Convert projection of given bbox.
//
// - `bbox` {Number} bbox in the form `[w, s, e, n]`.
// - `to` {String} projection of output bbox (WGS84|900913). Input bbox
// assumed to be the "other" projection.
// - `@return` {Object} bbox with reprojected coordinates.
SphericalMercator.prototype.convert = function(bbox, to) {
if (to === '900913') {
return this.forward(bbox.slice(0, 2)).concat(this.forward(bbox.slice(
2,
4)));
} else {
return this.inverse(bbox.slice(0, 2)).concat(this.inverse(bbox.slice(
2,
4)));
}
};
// Convert lon/lat values to 900913 x/y.
SphericalMercator.prototype.forward = function(ll) {
var xy = [
A * ll[0] * D2R,
A * Math.log(Math.tan((Math.PI * 0.25) + (0.5 * ll[1] * D2R)))
];
// if xy value is beyond maxextent (e.g. poles), return maxextent.
if (xy[0] > MAXEXTENT) xy[0] = MAXEXTENT;
if (xy[0] < -MAXEXTENT) xy[0] = -MAXEXTENT;
if (xy[1] > MAXEXTENT) xy[1] = MAXEXTENT;
if (xy[1] < -MAXEXTENT) xy[1] = -MAXEXTENT;
return xy;
};
// Convert 900913 x/y values to lon/lat.
SphericalMercator.prototype.inverse = function(xy) {
return [
(xy[0] * R2D / A), ((Math.PI * 0.5) - 2.0 * Math.atan(Math.exp(-xy[
1] /
A))) * R2D
];
};
return SphericalMercator;
})();
if (typeof module !== 'undefined' && typeof exports !== 'undefined') {
module.exports = exports = SphericalMercator;
}