添加矢量数据 - 使用 WFS 传输的 GML 格式（可能是错误？）

Question

我正在尝试通过查询提供 GML 数据的公开可用 WFS 服务器向我的 OpenLayers 地图添加要素。

// initalize the map
var map = new ol.Map({
    layers: [
        new ol.layer.Tile({
            // OpenLayers public map server
            source: new ol.source.OSM()
        }),
    ],
    target: 'map',
    view: new ol.View({
        // center on Murica
        center: [-10997148, 4569099],
        zoom: 4
    })
});

var xmlhttp = new XMLHttpRequest();

// execute this once the remote GML xml document has loaded
xmlhttp.onload = function() {

    console.log("GML XML document retrieved.  executing onload handler:");
    var format = new ol.format.GML3();

    var xmlDoc = xmlhttp.responseXML;

    console.log("you will see multiple features in the xml: ");
    console.log(xmlDoc);

    // Read and parse all features in XML document
    var features = format.readFeatures(xmlDoc, {
        featureProjection: 'EPSG:4326',
        dataProjection: 'EPSG:3857'
    });

    console.log("for some reason only a single feature will have been added: ")
    console.log(features);
    console.log("Why is this?");

    var vector = new ol.layer.Vector({
        source: new ol.source.Vector({
            format: format
        })
    });

    // Add features to the layer's source
    vector.getSource().addFeatures(features);

    map.addLayer(vector);
};

// configure a GET request
xmlhttp.open("GET", "http://geoint.nrlssc.navy.mil/dnc/wfs/DNC-WORLD/feature/merged?version=1.1.0&request=GetFeature&typename=DNC_APPROACH_LIBRARY_BOUNDARIES&srsname=3857",
   true);

// trigger the GET request
xmlhttp.send();

这是一个演示错误的 CodePen。

http://codepen.io/anon/pen/yamOEK

在这里你可以下载它打包成一个HTML文件： https://drive.google.com/open?id=0B6L3fhx8G3H_cmp1d3hHOXNKNHM

我可以使用有效的类型名称将具有多个功能的整个功能集合成功下载到我的变量 xmlDoc 中。然而，当我使用 format.ReadFeatures(xmlDoc) 时，OpenLayers GML 格式解析器似乎只从特征集合中提取单个特征，而它应该提取更多。

如果有人能看看他们是否能弄清楚我是在做一些愚蠢的错误还是 OpenLayers3 中的合法错误，那就太好了。非常感谢任何能够提供帮助的人！

Answer 1

添加了单个功能，因为整个文档都被读取，而不是 format.readFeatures(xmlDoc) 解析每个 feature.Here 是源代码：

    var vector;
    var map = new ol.Map({
        layers: [
            new ol.layer.Tile({
                source: new ol.source.OSM()
            }),
        ],
        target: 'map',
        view: new ol.View({
            center: [-8197020.761224195,8244563.818176944],
            zoom: 4
        })
    });

    var xmlhttp = new XMLHttpRequest();
    xmlhttp.onload = function() {
        var format = new ol.format.GML3();
        var xmlDoc = xmlhttp.responseXML;
        vector = new ol.layer.Vector({
            source: new ol.source.Vector({
                format: format
            })
        });

        for (var i = 1; i < xmlDoc.children[0].children.length; i++) {
            var features = format.readFeatures(xmlDoc.children[0].children[i], {
                featureProjection: 'EPSG:4326'
            });


            features.getGeometry().transform('EPSG:4326', 'EPSG:3857');
            vector.getSource().addFeature(features);
        }

        map.addLayer(vector);
        map.getView().fit(vector.getSource().getExtent(), map.getSize())
    };

    xmlhttp.open("GET", "http://geoint.nrlssc.navy.mil/dnc/wfs/DNC-WORLD/feature/merged?version=1.1.0&request=GetFeature&typename=DNC_APPROACH_LIBRARY_BOUNDARIES&srsname=3857",
        true);

    // trigger the GET request
    xmlhttp.send();

这是 CodePen 结果。 http://codepen.io/anon/pen/bwXrwJ

添加矢量数据 - 使用 WFS 传输的 GML 格式（可能是错误？）

Adding Vector Data - GML format with WFS Transport (possible bug?)

vector

openlayers-3

gml

web-feature-service