谷歌地图多边形自相交检测

Google Maps Polygons self intersecting detection

本文关键字：检测 自相交 多边形 谷歌地图      更新时间：2023-09-26

我正在尝试实现一个多边形自交算法从谷歌地图API V3多边形。
目标只是检测是或否，用户绘制的简单多边形是否自交叉。

我发现了这个非常有趣的链接，但它假设多边形顶点的坐标是geoJSON格式的。然而，这不是我的情况;我只能在polygoncomplete事件中使用polygon.getPath()检索多边形坐标。

我是这样获取坐标的:

google.maps.event.addDomListener(drawingManager, 'polygoncomplete', function(polygon)
{
    var polygonBounds = polygon.getPath();
    var coordinates = [];
    for(var i = 0 ; i < polygonBounds.length ; i++)
    {            
        vertice = {
                      "Latitude" : polygonBounds.getAt(i).lat(),
                      "Longitude" : polygonBounds.getAt(i).lng()
                  }
        coordinates.push(vertice );
    }
}

如何转换这些坐标，由polygon.getpath()到geoJSON格式?
有没有更好的方法来检测谷歌地图多边形是否自相交?如果是这样，你能分享一些代码示例，而不仅仅是一个数学解释吗?

PS:我已经看到了这个链接，但没有任何代码样本，我有点迷路了。

您不需要将它们转换为GeoJSON来使用jsts库，您需要将它们从google.maps.LatLng对象转换为jsts.geo . coordinates。而不是使用这个:

var geoJSON2JTS = function(boundaries) {
  var coordinates = [];
  for (var i = 0; i < boundaries.length; i++) {
    coordinates.push(new jsts.geom.Coordinate(
        boundaries[i][1], boundaries[i][0]));
  }
  return coordinates;
};

使用这个，它将把google.maps.Polygon路径中的坐标转换为JTS格式:

var googleMaps2JTS = function(boundaries) {
  var coordinates = [];
  for (var i = 0; i < boundaries.getLength(); i++) {
    coordinates.push(new jsts.geom.Coordinate(
        boundaries.getAt(i).lat(), boundaries.getAt(i).lng()));
  }
  return coordinates;
};

然后更改"findSelfIntersects"这样的:

/**
 * findSelfIntersects
 *
 * Detect self-intersections in a polygon.
 *
 * @param {object} google.maps.Polygon path co-ordinates.
 * @return {array} array of points of intersections.
 */
var findSelfIntersects = function(googlePolygonPath) {
  var coordinates = googleMaps2JTS(googlePolygonPath);
  var geometryFactory = new jsts.geom.GeometryFactory();
  var shell = geometryFactory.createLinearRing(coordinates);
  var jstsPolygon = geometryFactory.createPolygon(shell);
 
  // if the geometry is aleady a simple linear ring, do not
  // try to find self intersection points.
  var validator = new jsts.operation.IsSimpleOp(jstsPolygon);
  if (validator.isSimpleLinearGeometry(jstsPolygon)) {
    return;
  }
 
  var res = [];
  var graph = new jsts.geomgraph.GeometryGraph(0, jstsPolygon);
  var cat = new jsts.operation.valid.ConsistentAreaTester(graph);
  var r = cat.isNodeConsistentArea();
  if (!r) {
    var pt = cat.getInvalidPoint();
    res.push([pt.x, pt.y]);
  }
  return res;
};

概念验证小提琴(credit to HoffZ)

代码片段:

var mapOptions = {
  zoom: 16,
  center: new google.maps.LatLng(62.1482, 6.0696)
};
var drawingManager = new google.maps.drawing.DrawingManager({
  drawingControl: false,
  polygonOptions: {
    editable: true
  }
});
var googleMaps2JTS = function(boundaries) {
  var coordinates = [];
  for (var i = 0; i < boundaries.getLength(); i++) {
    coordinates.push(new jsts.geom.Coordinate(
      boundaries.getAt(i).lat(), boundaries.getAt(i).lng()));
  }
  coordinates.push(coordinates[0]);
  console.log(coordinates);
  return coordinates;
};
/**
 * findSelfIntersects
 *
 * Detect self-intersections in a polygon.
 *
 * @param {object} google.maps.Polygon path co-ordinates.
 * @return {array} array of points of intersections.
 */
var findSelfIntersects = function(googlePolygonPath) {
  var coordinates = googleMaps2JTS(googlePolygonPath);
  var geometryFactory = new jsts.geom.GeometryFactory();
  var shell = geometryFactory.createLinearRing(coordinates);
  var jstsPolygon = geometryFactory.createPolygon(shell);
  // if the geometry is aleady a simple linear ring, do not
  // try to find self intersection points.
  var validator = new jsts.operation.IsSimpleOp(jstsPolygon);
  if (validator.isSimpleLinearGeometry(jstsPolygon)) {
    return;
  }
  var res = [];
  var graph = new jsts.geomgraph.GeometryGraph(0, jstsPolygon);
  var cat = new jsts.operation.valid.ConsistentAreaTester(graph);
  var r = cat.isNodeConsistentArea();
  if (!r) {
    var pt = cat.getInvalidPoint();
    res.push([pt.x, pt.y]);
  }
  return res;
};

var map = new google.maps.Map(document.getElementById("map"), mapOptions);
drawingManager.setDrawingMode(google.maps.drawing.OverlayType.POLYGON);
drawingManager.setMap(map);
google.maps.event.addListener(drawingManager, 'polygoncomplete', function(polygon) {
  //var polyPath = event.overlay.getPath();
  var intersects = findSelfIntersects(polygon.getPath());
  console.log(intersects);
  if (intersects && intersects.length) {
    alert('Polygon intersects itself');
  } else {
    alert('Polygon does not intersect itself');
  }
});
#map {
  width: 500px;
  height: 400px;
}
<script src="https://maps.google.com/maps/api/js?libraries=drawing&key=AIzaSyCkUOdZ5y7hMm0yrcCQoCvLwzdM6M8s5qk"></script>
<script src="https://cdn.rawgit.com/bjornharrtell/jsts/gh-pages/1.4.0/jsts.min.js"></script>
<p>
  Draw a polygon on the map
</p>
<div id="map">
</div>

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