Computing the union 2 MKPolygons

问题

I am working on map applications with polygon MKOverlays. I have a requirement to merge (union) overlapping polygons.

Is there a well known algorithm to do this? Are there any free existing libraries/implementations that help with such geometry operations?

I have found the GEOS library, but apparently its licensing terms disallow use without distributing your source code. Is anyone else using this library. If yes, where can I find the way to include this in my Xcode project.

回答1:

The only free libraries I'm aware of are -

Clipper: http://angusj.com/delphi/clipper.php

Boost Polygon: http://www.boost.org/doc/libs/1_47_0/libs/polygon/doc/index.htm

Boost Geometry: http://trac.osgeo.org/ggl/

回答2:

Try gpc. They have several licences. Also there are similar libraries listed on their page.

回答3:

There is a great library RSClipperWrapper which is basically a wrapper for Clipper. There is even a great library comparison inside their website:

TL;DR, free library, error free and fast.

A few notes:

RSClipperWrapper takes CGPoint but fear not, you can pass lat/long into it and it will get the job done (tested and verified).

For convinice I've written an extension so we can just pass a custom Polygon array and get the merged polygons - if you're using MKPolygon or other type then don't forget adjust your type:

extension Clipper {
  static func union(polygons: [Polygon]) -> [Polygon] {
    let pointsPolygons = convert(polygons: polygons)
    let unionfied = Clipper.unionPolygons(pointsPolygons, withPolygons: pointsPolygons)
    return convert(pointsPolygons: unionfied)
   }

  static func convert(polygons: [Polygon]) -> [[CGPoint]] {
    var polygonsPoints: [[CGPoint]] = []
    for polygon in polygons {
        var points: [CGPoint] = []
        for location in polygon.locations {
            points.append(CGPoint(x: location.coordinate.latitude, y: location.coordinate.longitude))
        }
        polygonsPoints.append(points)
    }
    return polygonsPoints
   }

  static func convert(pointsPolygons: [[CGPoint]]) -> [Polygon] {
    var polygons: [Polygon] = []
    for pointsPolygon in pointsPolygons {
        var locations: [CLLocation] = []
        for point in pointsPolygon {
            locations.append(CLLocation(latitude: CLLocationDegrees(point.x), longitude: CLLocationDegrees(point.y)))
        }
        let polygon = Polygon(locations: locations)
        polygons.append(polygon)
    }
    return polygons
 }
}

来源：https://stackoverflow.com/questions/6796458/computing-the-union-2-mkpolygons

标签

objective-c

ios

geometry

polygon