test/data/map/encode.js

/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements.  See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership.  The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License.  You may obtain a copy of the License at
*
*   http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied.  See the License for the
* specific language governing permissions and limitations
* under the License.
*/


function encode(json) {
    if (json.UTF8Encoding) {
        return;
    }

    json.UTF8Encoding = true;

    var features = json.features;

    features.forEach(function (feature){
        var encodeOffsets = feature.geometry.encodeOffsets = [];
        var coordinates = feature.geometry.coordinates;
        if (feature.geometry.type === 'MultiPolygon') {
            coordinates.forEach(function (polygon, idx1){
                encodeOffsets[idx1] = [];
                polygon.forEach(function (coordinate, idx2) {
                    coordinates[idx1][idx2] = encodeRing(
                        coordinate, encodeOffsets[idx1][idx2] = []
                    );
                });
            });
        }
        else if (feature.geometry.type == 'Polygon'
            || feature.geometry.type == 'MultiLineString'
        ) {
            coordinates.forEach(function (coordinate, idx){
                coordinates[idx] = encodeRing(
                    coordinate, encodeOffsets[idx] = []
                );
            });
        }
        else if (feature.geometry.type === 'LineString') {
            feature.geometry.coordinates = encodeRing(coordinates, encodeOffsets)
        }
    });

    return json;
}

function encodeRing(coordinates, encodeOffsets) {

    var result = '';

    var prevX = quantize(coordinates[0][0]);
    var prevY = quantize(coordinates[0][1]);
    // Store the origin offset
    encodeOffsets[0] = prevX;
    encodeOffsets[1] = prevY;

    for (var i = 0; i < coordinates.length; i++) {
        var point = coordinates[i];
        result += encodePoint(point[0], prevX);
        result += encodePoint(point[1], prevY);

        prevX = quantize(point[0]);
        prevY = quantize(point[1]);
    }

    return result;
}

function quantize(val) {
    return Math.ceil(val * 1024);
}

function encodePoint(val, prev){
    // Quantization
    val = quantize(val);
    // var tmp = val;
    // Delta
    var delta = val - prev;

    if (((delta << 1) ^ (delta >> 15)) + 64 === 8232) {
        //WTF, 8232 will get syntax error in js code
        delta--;
    }
    // ZigZag
    delta = (delta << 1) ^ (delta >> 15);
    // add offset and get unicode
    return String.fromCharCode(delta + 64);
}

// Export for testing.
if (typeof module !== 'undefined') {
    module.exports = encode;
}
else {
    window.encodeGeoJSON = encode;
}