如何在OpenLayers 3中繪製多部分幾何圖形？

Question

ol.interaction.Draw具有Point，LineString，Polygon，MultiPoint，MultiLineString，MultiPolygon和Circle作爲類型選項。我無法弄清楚的是如何真正繪製例如一個包含幾個單個多邊形的MultiPolygon。 Here's a demo控制檯記錄一個有效的GeoJSON字符串，但只包含一個單一的多邊形。

相關代碼：

// create draw interaction and add it to the map: 
drawInteraction = new ol.interaction.Draw({ source:vectorSource, type:"MultiPolygon" }); 
map.addInteraction(drawInteraction); 

// define GeoJSON format: 
var formatGeoJSON = new ol.format.GeoJSON(); 

// set listener on "drawend": 
drawInteraction.on("drawend", function(e) { 
    // get feature: 
    var feature = e.feature; 
    // clone feature: 
    var featureClone = feature.clone(); 
    // transform cloned feature to WGS84: 
    featureClone.getGeometry().transform('EPSG:3857', 'EPSG:4326'); 
    // get GeoJSON of feature: 
    var geojson = formatGeoJSON.writeFeature(featureClone); 
    // log: 
    console.log(geojson); 
}); 

Answer 1

我建議你做這樣的事情：

var drawInteraction = new ol.interaction.Draw({ 
    source: vectorSource, 
    type: "Polygon" 
}); 
map.addInteraction(drawInteraction); 

var multiPolygon = new ol.geom.MultiPolygon([]); 
drawInteraction.on('drawend', function(e) { 
    var 
     feature = e.feature, 
     poly = feature.getGeometry() 
    ; 
    multiPolygon.appendPolygon(poly); 
    updateGeojson(); 
}); 
function updateGeojson(){ 
    var 
     formatGeoJSON = new ol.format.GeoJSON(), 
     cloned = multiPolygon.clone() 
    ; 
    cloned.transform('EPSG:3857', 'EPSG:4326'); 
    var geojson = formatGeoJSON.writeGeometry(cloned); 
    console.info(geojson); 
} 

https://jsfiddle.net/jonataswalker/epyuLy7x/