92 lines
2.9 KiB
JavaScript
92 lines
2.9 KiB
JavaScript
var Point = function(x, y) {
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this.x = x || 0;
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this.y = y || 0;
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};
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function clamp(value, optMin, optMax) {
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if (optMin !== null) value = Math.max(value, optMin);
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if (optMax !== null) value = Math.min(value, optMax);
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return value;
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}
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function degreesToRadians(deg) {
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return deg * (Math.PI / 180);
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}
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function radiansToDegrees(rad) {
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return rad / (Math.PI / 180);
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}
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var MercatorProjection = function() {
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// this._tileSize = L.Browser.retina ? 512 : 256;
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this._tileSize = 256;
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this._pixelOrigin = new Point(this._tileSize / 2, this._tileSize / 2);
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this._pixelsPerLonDegree = this._tileSize / 360;
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this._pixelsPerLonRadian = this._tileSize / (2 * Math.PI);
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};
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MercatorProjection.prototype._fromLatLonToPoint = function(lat, lon) {
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var point = new Point(0, 0);
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var origin = this._pixelOrigin;
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point.x = origin.x + lon * this._pixelsPerLonDegree;
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// NOTE(appleton): Truncating to 0.9999 effectively limits latitude to
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// 89.189. This is about a third of a tile past the edge of the world
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// tile.
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var siny = clamp(Math.sin(degreesToRadians(lat)), -0.9999, 0.9999);
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point.y = origin.y + 0.5 * Math.log((1 + siny) / (1 - siny)) * -this._pixelsPerLonRadian;
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return point;
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};
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MercatorProjection.prototype._fromPointToLatLon = function(point) {
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var me = this;
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var origin = me._pixelOrigin;
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var lon = (point.x - origin.x) / me._pixelsPerLonDegree;
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var latRadians = (point.y - origin.y) / -me._pixelsPerLonRadian;
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var lat = radiansToDegrees(2 * Math.atan(Math.exp(latRadians)) - Math.PI / 2);
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return { lat:lat, lon:lon };
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};
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MercatorProjection.prototype._tilePixelPos = function(tileX, tileY) {
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return {
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x: tileX*this._tileSize,
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y: tileY*this._tileSize
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};
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};
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MercatorProjection.prototype.tilePixelBBox = function(x, y, zoom, px, py, res) {
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res = res || 1.0;
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var numTiles = 1 <<zoom;
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var inc = res/numTiles;
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px = (x*this._tileSize + px)/numTiles;
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py = (y*this._tileSize + py)/numTiles;
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return [
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this._fromPointToLatLon(new Point(px, py + inc)),
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this._fromPointToLatLon(new Point(px + inc, py))
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];
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};
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MercatorProjection.prototype.tileBBox = function(x, y, zoom, bufferSize) {
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var numTiles = 1 <<zoom;
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bufferSize = bufferSize || 0;
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var inc = (this._tileSize + bufferSize*2)/numTiles;
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var px = (x*this._tileSize - bufferSize )/numTiles;
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var py = (y*this._tileSize - bufferSize )/numTiles;
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return [
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this._fromPointToLatLon(new Point(px, py + inc)),
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this._fromPointToLatLon(new Point(px + inc, py))
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];
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};
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MercatorProjection.prototype.latLonToTilePoint = function(lat, lon, tileX, tileY, zoom) {
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var numTiles = 1 <<zoom;
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var worldCoordinate = this._fromLatLonToPoint(lat, lon);
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var pixelCoordinate = new Point(worldCoordinate.x*numTiles, worldCoordinate.y*numTiles);
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var tilePixelPos = this._tilePixelPos(tileX, tileY);
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return new Point(Math.round(pixelCoordinate.x-tilePixelPos.x), Math.round(pixelCoordinate.y-tilePixelPos.y));
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};
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module.exports = MercatorProjection;
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