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/* -*- Mode: JS2; indent-tabs-mode: nil; js2-basic-offset: 4 -*- */
/* vim: set et ts=4 sw=4: */
/*
* Copyright (c) 2013 Mattias Bengtsson.
*
* GNOME Maps is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by the
* Free Software Foundation; either version 2 of the License, or (at your
* option) any later version.
*
* GNOME Maps is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* for more details.
*
* You should have received a copy of the GNU General Public License along
* with GNOME Maps; if not, see <http://www.gnu.org/licenses/>.
*
* Author: Jussi Kukkonen <jku@goto.fi>
* Mattias Bengtsson <mattias.jc.bengtsson@gmail.com>
*/
// Google encoded polyline decoder
// https://developers.google.com/maps/documentation/utilities/polylinealgorithm
import Shumate from 'gi://Shumate';
function _decodeValue(data, index) {
let b;
let shift = 0;
let value = 0;
do {
// 63 added to keep string printable
b = data.charCodeAt(index++) - 63;
// Get 5 bits at a time until hit the end of value
// (which is not OR'd with 0x20)
value |= (b & 0x1f) << shift;
shift += 5;
} while (b >= 0x20);
// negative values are encoded as two's complement
let ret_val = ((value & 1) ? ~(value >> 1) : (value >> 1));
return [ret_val, index];
}
export function decode(data) {
let length = data.length;
let polyline = [];
let index = 0;
let lat = 0;
let lon = 0;
while (index < length) {
let latdelta, londelta;
[latdelta, index] = _decodeValue(data, index);
[londelta, index] = _decodeValue(data, index);
// first value is absolute, rest are relative to previous value
lat += latdelta;
lon += londelta;
polyline.push(new Shumate.Coordinate({
latitude: lat * 1e-5,
longitude: lon * 1e-5
}));
}
return polyline;
}
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