Javascript 从Google地图提取多段线到GeoJSON

我有一张谷歌地图。当用户单击时，它会放置一个“开始”标记。第二次单击将在第一次单击和第二次单击之间生成一条多段线，并添加一个“结束”标记。第三次单击将向多段线添加另一个数据点，并将“结束”标记移动到最近一次单击。没什么特别的：

map = new google.maps.Map(document.getElementById('map'), {
            center: {lat: -34.397, lng: 150.644},
            zoom: 13
});
map.addListener('click', insertDataPoint);

polyline = new google.maps.Polyline({
            strokeColor: '#000000',
            strokeOpacity: 0.7,
            strokeWeight: 3
}); 
polyline.setMap(map);

plots = [];

... // Bunch of other code that isn't important

function insertDataPoint(e) {   
    var path = polyline.getPath();
    path.push(e.latLng);

    // Logic to set up marker or circle 
    if (plots.length == 0) {
        // Case: first click
        startMarker.setPosition(e.latLng);
        startMarker.setMap(map);
        plots.push(startMarker);                        

    } else {
        if (plots.length != 1) {
            // Case: we have intermediate points between start and end
            var plot = plots.pop();

            var marker = new google.maps.Marker({
                position: plot.getPosition(),
                icon: {
                    path: google.maps.SymbolPath.CIRCLE,
                    fillColor: '#ffffff',
                    fillOpacity: 0.6,
                    strokeColor: '#ffffff',
                    strokeOpacity: 0.8,
                    strokeWeight: 2,
                    scale: 3
                }
            });
            marker.setMap(map);
            plots.push(marker);
        }
        // Case: add an end marker
        endMarker.setPosition(e.latLng);
        if (plots.length == 1) {
            endMarker.setMap(map);
        }
        plots.push(endMarker);
    }
}

我想得到GeoJSON格式的打印点。我知道Google最近发布了带有.toGeoJson（）调用的数据层API，但很自然，数据是空的，因为它没有添加到数据层：

map.data.toGeoJson( function(data) {
    alert(JSON.stringify(data)); // {"type":"FeatureCollections", "features":[]}

function exportGeoJson() {
    var geoJson = {
        "type": "FeatureCollection",
            "features": []
    };
    var polylineFeature = {
        "type": "Feature",
            "geometry": {
            "type": "LineString",
                "coordinates": []
        },
            "properties": {}
    };
    for (var i = 0; i < polyline.getPath().getLength(); i++) {
        var pt = polyline.getPath().getAt(i);
        polylineFeature.geometry.coordinates.push([
        pt.lng(), pt.lat()]);
    }
    geoJson.features.push(polylineFeature);
    document.getElementById('geojson').value = JSON.stringify(geoJson);
    polyline.setPath([]);
    map.data.addGeoJson(geoJson);
    // Set the stroke width, and fill color for each polygon
    map.data.setStyle({
        strokeColor: 'green',
        strokeWeight: 2
    });
    map.data.toGeoJson( function(data) {
      document.getElementById('exported').value=JSON.stringify(data)
    });

}

所以问题是，我如何将数据——标记和多段线——添加到数据层，以便获得漂亮的GeoJSON

---

注意--我知道数据层具有允许用户在地图上绘制的功能，但我需要按照自己的方式进行绘制。

这将创建表示多段线的geoJSON，并将其添加到数据层：

map.data.toGeoJson( function(data) {
    alert(JSON.stringify(data)); // {"type":"FeatureCollections", "features":[]}

function exportGeoJson() {
    var geoJson = {
        "type": "FeatureCollection",
            "features": []
    };
    var polylineFeature = {
        "type": "Feature",
            "geometry": {
            "type": "LineString",
                "coordinates": []
        },
            "properties": {}
    };
    for (var i = 0; i < polyline.getPath().getLength(); i++) {
        var pt = polyline.getPath().getAt(i);
        polylineFeature.geometry.coordinates.push([
        pt.lng(), pt.lat()]);
    }
    geoJson.features.push(polylineFeature);
    document.getElementById('geojson').value = JSON.stringify(geoJson);
    polyline.setPath([]);
    map.data.addGeoJson(geoJson);
    // Set the stroke width, and fill color for each polygon
    map.data.setStyle({
        strokeColor: 'green',
        strokeWeight: 2
    });
    map.data.toGeoJson( function(data) {
      document.getElementById('exported').value=JSON.stringify(data)
    });

}

出口

这将创建表示多段线的geoJSON，并将其添加到数据层：

map.data.toGeoJson( function(data) {
    alert(JSON.stringify(data)); // {"type":"FeatureCollections", "features":[]}

function exportGeoJson() {
    var geoJson = {
        "type": "FeatureCollection",
            "features": []
    };
    var polylineFeature = {
        "type": "Feature",
            "geometry": {
            "type": "LineString",
                "coordinates": []
        },
            "properties": {}
    };
    for (var i = 0; i < polyline.getPath().getLength(); i++) {
        var pt = polyline.getPath().getAt(i);
        polylineFeature.geometry.coordinates.push([
        pt.lng(), pt.lat()]);
    }
    geoJson.features.push(polylineFeature);
    document.getElementById('geojson').value = JSON.stringify(geoJson);
    polyline.setPath([]);
    map.data.addGeoJson(geoJson);
    // Set the stroke width, and fill color for each polygon
    map.data.setStyle({
        strokeColor: 'green',
        strokeWeight: 2
    });
    map.data.toGeoJson( function(data) {
      document.getElementById('exported').value=JSON.stringify(data)
    });

}

出口