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index.js
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index.js
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'use strict';
/**
* convert base of a number.
* example:
* convertBase(111).from(2).to(10); // 7
*/
function convertBase(value) {
return {
from: function(baseFrom) {
return {
to: function(baseTo) {
return parseInt(value, baseFrom).toString(baseTo);
}
};
}
};
}
/**
* fill value with leading zeros
*/
function zfill(value, length) {
var s = value + "";
while (s.length < length) {
s = "0" + s;
}
return s;
}
/**
* Compute quad key string for given x/y tile coordinates and zoom level
*
* @param {integer} x tile x
* @param {integer} y tile y
* @param {integer} z zoom level
* @return {string} quad key
*/
exports.tile2key = function tile2key(x, y, z) {
var x_bin = convertBase(x).from(10).to(2);
var y_bin = convertBase(y).from(10).to(2);
x_bin = zfill(x_bin, z);
y_bin = zfill(y_bin, z);
// interleave bits
var quadkey = [];
for (var i = 0; i < z; i++) {
// rows, i.e., y-axis, comes first
quadkey.push(y_bin.charAt(i));
quadkey.push(x_bin.charAt(i));
}
// convert quadkey to base-4 number, maintaining leading zeros (!)
quadkey = quadkey.join("");
quadkey = convertBase(quadkey).from(2).to(4);
// add leading zeros if needed
quadkey = zfill(quadkey, z);
return quadkey
};
/**
* Inverse of tile2key
*
* @param {string} quadkey
* @return {object} {x: x, y: y, z: z}
*/
exports.key2tile = function key2tile(quadkey) {
var zoom = quadkey.length;
// convert quadkey to binary
var quadkey_bin = convertBase(quadkey).from(4).to(2);
// it's crucial to maintain leading zeros
quadkey_bin = zfill(quadkey_bin, zoom * 2);
// de-interleave bits
var x_bin = []; // "binary" (string) array
var y_bin = [];
var i = 0;
while (i < quadkey_bin.length) {
// recall that y-axis comes first
y_bin.push(quadkey_bin.charAt(i));
i++;
x_bin.push(quadkey_bin.charAt(i));
i++;
}
x_bin = x_bin.join("");
y_bin = y_bin.join("");
var x = convertBase(x_bin).from(2).to(10);
var y = convertBase(y_bin).from(2).to(10);
var coords = {
x: x,
y: y,
z: zoom
}
return coords;
};