Runtime Line Intersection Points

AGSPolyline+Intersection.swift

extension AGSPolyline {
    func intersectionsWith(line:AGSPolyline) -> [AGSPoint] {
        var outPoints = [AGSPoint]()
        let threshold = 1E-10
        if let lineCut = AGSGeometryEngine.union(ofGeometry1: self, geometry2: line), let lineE = AGSGeometryEngine.intersection(ofGeometry1: self, geometry2: lineCut) as? AGSPolyline {
            print("LineE: \(lineE)")
            for part in lineE.parts.array() {
                for i in 0 ..< part.points.count {
                    let point = part.points.point(at: i)
                    let distance = AGSGeometryEngine.distanceBetweenGeometry1(point, geometry2: line)
                    if distance < threshold {
                        outPoints.append(point)
                    }
                }
            }
        }
        
        return outPoints
    }
}

Test.swift

let lineAB = AGSPolyline(points: [AGSPointMakeWGS84(0, 0), AGSPointMakeWGS84(10, 10)])
let lineCD = AGSPolyline(points: [AGSPointMakeWGS84(0, 10), AGSPointMakeWGS84(8.5, 7), AGSPointMakeWGS84(4, 6), AGSPointMakeWGS84(10, 0)])

let points = lineAB.intersectionsWith(line: lineCD)
print("Intersections at: \(points)")

This relies on an observed property of the generated output Polyline that it has vertices wherever it's crossed by the second geometry. In short, I get the coincident segment of the two polylines, which is effectively lineAB but with extra vertices along its length (wherever lineCD crossed it), and return only the vertices that are also on lineCD.

Note: This may produce additional results if lineCD has a segment that is directly aligned with a part or all of lineAB and which has in-line vertices. In the example below, you may not expect to see E4, but the above algorithm will return it.

It should only be a problem in very specific use cases.

This relates to this GeoNet discussion.