转换折线到GeoJSON的

Question

我有一系列的（编码或解码）从谷歌地图/开放街道地图服务拍摄的折线。

例如：

var polylines = ["kclaG|i_qLe@i@{AgBu@_AsCyCiBmBMMW[eCiC}A_BEEeBiB{@}@MW]a@a@e@]a@IGGG_AgAm@i@MOYYMEQSCCi@k@KKu@y@{A}Ay@cA{@{@eBiBOMe@k@_@a@e@e@QQY[cAkAUWMOUWu@w@AACCYY?AMKUUSSSQ]]GGECCCECA?AAA?A?C?G?WB" 
     ,"yfnaGld}pL?e@?]AuDAgA?KAkBGqG?{C?_B?S?aC?[?]A}A?wAASAQ" 
     ,"qmnaGlxxpLn@tEL~@"] 

我想将这些存储为GeoJSON的。我发现很多通过Leaflet等工具呈现GeoJSON的包，但是我很难找到可以将多段线导出到GeoJSON的包。

做任何像这样的解决办法是存在还是有，我应该寻找到这样我就可以写工具MYSET的GeoJSON的标准的特定子集？

附注：我最终要KML或SHP文件。我打算使用http://ogre.adc4gis.com/将GeoJSON转换为SHP。

Answer 1

您正在寻找的GeoJSON的LineString的几何类型。虽然算法有点复杂，但有一个a project on Github提供了JavaScript中的功能。您应该能够轻松将其转换为您选择的语言。我还将这些功能封装到JSFiddle中，以便您可以将其用作在线工具。

您会在https://jsfiddle.net/ivansams/tw7qLvh4/2/找到该工具 - 您可以将编码后的折线粘贴到“编码折线”中，然后单击“解码”，这将返回一个GeoJSON LineString。下面的代码是由于StackOverflow的规则要求JSFiddle伴随有代码，但是在Github项目站点上获取最新的代码。

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; 
}