turf.js OpenLayers3 Draw 中自相交多边形的相交误差

Question

我正在使用 OpenLayers3 ol.interaction.Draw 让用户在地图上绘制一个形状，通过单击顶点或通过 Shift+Drag 绘制自由多边形（这对我的应用程序很重要）。绘制形状后，我使用 turf.js 将绘制的形状与客户端中的 WFS 层进行比较，运行 intersect() 以查看 WFS 特征是否与绘制的形状相交。但是，如果手绘形状有最轻微的自相交，turf.js intersect() 函数将失败并出现以下错误（第 326 行是我调用 intersect() 的地方）。

turf.min.js:9 Uncaught [object Object]
getResultGeometry @ turf.min.js:9
si.overlayOp @ turf.min.js:9
intersection @ turf.min.js:15
e.exports @ turf.min.js:16
(anonymous function) @ main.js:326

以下是我的代码草图。

var features = new ol.Collection();

var vs = new ol.source.Vector({
  format: new ol.format.GeoJSON(),
  url: function(extent) {
    return XXXXXX;
  },
  strategy: ol.loadingstrategy.bbox
});

features.on('add', function() {
  vs.forEachFeatureIntersectingExtent(extent, function(feature) {
    // use to turf.js to intersect each feature with drawn feature
    var bt = gjformat.writeFeatureObject(feature, {rightHanded: false});
    var dt = gjformat.writeFeatureObject(features.item(0), {rightHanded: false} );

    var intersection = turf.intersect(bt, dt);
  }
});

我试过 turf.js simplify() 和 ol.geom.Geometry.simplify() 都没有用。有没有人对让 turf.js intersect() 处理手绘的自相交多边形有任何建议？或者有一种方法可以删除运行交点之前的自交点？

Answer 1

您至少可以警告用户注意自相交。这些可以用 JSTS 检测到。参见 Google Maps Polygons self intersecting detection. Removing self-intersections is harder, but it should also be possible with JSTS: 。

Answer 2

受到答案的启发（感谢@ahocevar 的领导），我将解决方案移植到 turf.js。将具有自相交的绘制要素缓冲 0 会删除较小的自相交多边形，并为您留下运行到 intersect().

的干净要素

    features.on('add', function() {
      vs.forEachFeatureIntersectingExtent(extent, function(feature) {
        // create geojson of wfs features and drawn feature
        var bt = gjformat.writeFeatureObject(feature, {rightHanded: false});
        var dt = gjformat.writeFeatureObject(features.item(0), {rightHanded: false} );

        // check for kinks in the drawn feature
        var kinks = turf.kinks(dt);
        var dtf;

        if(kinks.features.length > 0) {
          // if there are self-intersections, buffer by 0 to get rid of them
          dtf = turf.buffer(dt, 0, 'meters');
        } else {
          // if there are no self-intersection, intersect by unbuffered features
          dtf = dt; 
        }

        var intersection = turf.intersect(bt, dtf);
      }
    });

turf.js OpenLayers3 Draw 中自相交多边形的相交误差

turf.js Intersect Error for Self-intersecting Polygons from OpenLayers3 Draw

javascript

openlayers-3

turfjs