Check if a point is in polygon (maps)

问题:

I'm trying to check if a point is in polygon.
At the moment I have try with this function

pointInPolygon:function (point,polygon){
    var i;
    var j=polygon.length-1;
    var inPoly=false;
    var lon = point.longitude;
    var lat = point.latitude;
    for (i=0; i<polygon.length; i++)
    {
        if (polygon[i][0]<lon && polygon[j][0]>=lon|| polygon[j][0]<lon && polygon[i][0]>=lon){
            if (polygon[i][0]+(lon-polygon[i][0])/(polygon[j][0]-polygon[i][0])*(polygon[j][1]-polygon[i][1])<lat){
                inPoly=!inPoly;
            }
        }
        j=i;
    }
    return inPoly;
}

... this function is seems to work on simple polygon ( http://jsfiddle.net/zTmr7/3/ ) but it won't work for me... here is sample data of a polygon:

polygon: Array[14]
Array[2]
        0: "-120.190625"
        1: "29.6614549946937"
Array[2]
        0: "-116.87275390625"
        1: "32.6320990313992"
Array[2]
        0: "-116.60908203125"
        1: "34.0363970332393"
Array[2]
        0: "-120.89375"
        1: "41.9203747676428"
Array[2]
        0: "-114.74140625"
        1: "45.784484644005"
Array[2]
        0: "-115.971875"
        1: "48.6489780115889"
Array[2]
        0: "-132.758984375"
        1: "59.9891712248332"
Array[2]
        0: "-162.5099609375"
        1: "68.919753529737"
Array[2]
        0: "-168.6623046875"
        1: "68.9828872543805"
Array[2]
        0: "-168.4865234375"
        1: "64.2551601036027"
Array[2]
        0: "-179.874356794357"
        1: "51.0915874974707"
Array[2]
        0: "-179.999916362762"
        1: "13.1823178795562"
Array[2]
        0: "-143.8771484375"
        1: "19.9962034117847"
Array[2]
        0: "-120.190625"
        1: "29.6614549946937"  

Maybe you can help... thanks in advance

PS. solution must be especially for Bing maps or universal solution...

回答1:

The Google maps API does not already provide a method for checking points in polygons. After researching a bit I stumbled across the Ray-casting algorithm which will determine if an X-Y coordinate is inside a plotted shape. This will translate to latitude and longitude. The following extends the google.maps.polygon.prototype to use this algorithm. Simply include this code at a point in the code after google.maps has loaded:

google.maps.Polygon.prototype.Contains = function(point) {
  var crossings = 0, path = this.getPath();

  // for each edge
  for (var i=0; i < path.getLength(); i++) {
      var a = path.getAt(i),
          j = i + 1;
      if (j >= path.getLength()) {
          j = 0;
      }
      var b = path.getAt(j);
      if (rayCrossesSegment(point, a, b)) {
        crossings++;
      }
  }

  // odd number of crossings?
  return (crossings % 2 == 1);

  function rayCrossesSegment(point, a, b) {
    var px = point.lng(),
        py = point.lat(),
        ax = a.lng(),
        ay = a.lat(),
        bx = b.lng(),
        by = b.lat();
    if (ay > by) {
        ax = b.lng();
        ay = b.lat();
        bx = a.lng();
        by = a.lat();
    }
    // alter longitude to cater for 180 degree crossings
    if (px < 0) { px += 360 };
    if (ax < 0) { ax += 360 };
    if (bx < 0) { bx += 360 };

    if (py == ay || py == by) py += 0.00000001;
    if ((py > by || py < ay) || (px > Math.max(ax, bx))) return false;
    if (px < Math.min(ax, bx)) return true;

    var red = (ax != bx) ? ((by - ay) / (bx - ax)) : Infinity;
    var blue = (ax != px) ? ((py - ay) / (px - ax)) : Infinity;
    return (blue >= red);
  }
};

Here we have extended the functionality of google.maps.Polygon by defining a function with name ‘Contains’ which can be used to determine whether the latitude longitude provided in function parameter are within the polygon or not. Here we make use of Ray-casting algorithm and developed a function using the same. After doing this much of exercise now, we can check a point as follows:

var point = new google.maps.LatLng(52.05249047600099, -0.6097412109375); var polygon = new google.maps.Polygon({path:[INSERT_PATH_ARRAY_HERE]}); if (polygon.Contains(point)) { // point is inside polygon }

For complete code and demo please go to: http://counsellingbyabhi.blogspot.in/2013/01/google-map-check-whether-point-latlong.html

回答2:

The first if statement looks good - you're checking to see if the longitude of the point lies within the longitude of the polygon segment.

The second if should be interpolating the intercept of the segment with the exact longitude of the point, and determining if that intercept is above or below the point. I don't think that is what it is doing, due to a simple typo.

if (polygon[i][1]+(lon-polygon[i][0])/(polygon[j][0]-polygon[i][0])*(polygon[j][1]-polygon[i][1])<lat){
               ^

You should also include a separate case when polygon[i][0]==polygon[j][0] so that you don't get a divide-by-zero error.

回答3:

You can use my clone of the libkml variant which I have mirrored in github here: https://github.com/gumdal/libkml-pointinpolygon

With help of the author of this open source, a module is designed which will indicate whether the given point is inside the KML polygon or not. Make sure that you check the branch "libkml-git" and not the "master" branch of the git sources. The class you would be interested in is "pointinpolygon.cc". It is C++ source code which you can include inside your project and build it along with your project.

Edit - The solution for point in polygon problem is independent of what map it is overlayed on.

回答4:

true|false = google.maps.geometry.poly.containsLocation(googlePoint, googlePoly);