android – 识别点是否在多边形中

参考http://en.wikipedia.org/wiki/Point_in_polygon论文的射线铸造

private Boolean isPoinTinPolygon(LatLng tap,ArrayList<LatLng> vertices) {
        int intersectCount = 0;
        for (int j = 0; j < vertices.size() - 1; j++) {
            if (rayCasTintersect(tap,vertices.get(j),vertices.get(j + 1))) {
                intersectCount++;
            }
        }

        return ((intersectCount % 2) == 1); // odd = inside,even = outside;
    }

    private Boolean rayCasTintersect(LatLng tap,LatLng vertA,LatLng vertB) {

        double aY = vertA.latitude;
        double bY = vertB.latitude;
        double aX = vertA.longitude;
        double bX = vertB.longitude;
        double pY = tap.latitude;
        double pX = tap.longitude;

        if ((aY > pY && bY > pY) || (aY < pY && bY < pY)
                || (aX < pX && bX < pX)) {
            return false; // a and b can't both be above or below pt.y,and a or
                            // b must be east of pt.x
        }

        double m = (aY - bY) / (aX - bX); // Rise over run
        double bee = (-aX) * m + aY; // y = mx + b
        double x = (pY - beE) / m; // algebra is neat!

        return x > pX;
    }