I am a complete novice at coding and am trying to return a decoded polyline in array of (lat;lng) from an encoded polyline string.
I found a similar post here Converting encoded polylines into GeoJSON and KML files?
Which led me unto this.
function decode() {
var encodedPolyline = document.getElementById("encoded-polyline").value;
document.getElementById("geojson").value = encodedPolyline;
var coords = polyline.toGeoJSON(encodedPolyline);
document.getElementById("geojson").value = JSON.stringify(coords);
}
var polyline = {};
function encode(current, previous, factor) {
current = Math.round(current * factor);
previous = Math.round(previous * factor);
var coordinate = current - previous;
coordinate <<= 1;
if (current - previous < 0) {
coordinate = ~coordinate;
}
var output = '';
while (coordinate >= 0x20) {
output += String.fromCharCode((0x20 | (coordinate & 0x1f)) + 63);
coordinate >>= 5;
}
output += String.fromCharCode(coordinate + 63);
return output;
}
/**
* Decodes to a [latitude, longitude] coordinates array.
*
* This is adapted from the implementation in Project-OSRM.
*
* @param {String} str
* @param {Number} precision
* @returns {Array}
*
* @see https://github.com/Project-OSRM/osrm-frontend/blob/master/WebContent/routing/OSRM.RoutingGeometry.js
*/
polyline.decode = function(str, precision) {
var index = 0,
lat = 0,
lng = 0,
coordinates = [],
shift = 0,
result = 0,
byte = null,
latitude_change,
longitude_change,
factor = Math.pow(10, precision || 5);
// Coordinates have variable length when encoded, so just keep
// track of whether we've hit the end of the string. In each
// loop iteration, a single coordinate is decoded.
while (index < str.length) {
// Reset shift, result, and byte
byte = null;
shift = 0;
result = 0;
do {
byte = str.charCodeAt(index++) - 63;
result |= (byte & 0x1f) << shift;
shift += 5;
} while (byte >= 0x20);
latitude_change = ((result & 1) ? ~(result >> 1) : (result >> 1));
shift = result = 0;
do {
byte = str.charCodeAt(index++) - 63;
result |= (byte & 0x1f) << shift;
shift += 5;
} while (byte >= 0x20);
longitude_change = ((result & 1) ? ~(result >> 1) : (result >> 1));
lat += latitude_change;
lng += longitude_change;
coordinates.push([lat / factor, lng / factor]);
}
return coordinates;
};
/**
* Encodes the given [latitude, longitude] coordinates array.
*
* @param {Array.<Array.<Number>>} coordinates
* @param {Number} precision
* @returns {String}
*/
polyline.encode = function(coordinates, precision) {
if (!coordinates.length) {
return '';
}
var factor = Math.pow(10, precision || 5),
output = encode(coordinates[0][0], 0, factor) + encode(coordinates[0][1], 0, factor);
for (var i = 1; i < coordinates.length; i++) {
var a = coordinates[i],
b = coordinates[i - 1];
output += encode(a[0], b[0], factor);
output += encode(a[1], b[1], factor);
}
return output;
};
function flipped(coords) {
var flipped = [];
for (var i = 0; i < coords.length; i++) {
flipped.push(coords[i].slice().reverse());
}
return flipped;
}
/**
* Encodes a GeoJSON LineString feature/geometry.
*
* @param {Object} geojson
* @param {Number} precision
* @returns {String}
*/
polyline.fromGeoJSON = function(geojson, precision) {
if (geojson && geojson.type === 'Feature') {
geojson = geojson.geometry;
}
if (!geojson || geojson.type !== 'LineString') {
throw new Error('Input must be a GeoJSON LineString');
}
return polyline.encode(flipped(geojson.coordinates), precision);
};
/**
* Decodes to a GeoJSON LineString geometry.
*
* @param {String} str
* @param {Number} precision
* @returns {Object}
*/
polyline.toGeoJSON = function(str, precision) {
var coords = polyline.decode(str, precision);
return {
type: 'LineString',
coordinates: flipped(coords)
};
};
if (typeof module === 'object' && module.exports) {
module.exports = polyline;
}
All I am trying to achieve is passing the string directly in the code and returning the result to console.
