CCW) by finding the lower left corner point and determining if the y value of the next point is equal to (CCW) or greater (CW).

Question

Once you have the orientation you can iterate through the edges to determine their type.

With

Obviously the type for CW polygons is reversed.

enum EdgeType {TOP, BOTTOM, LEFT, RIGHT, EMPTY}

public EdgeType orthoEdgeTypeCCW(double x0, double y0, double x1, double y1)
{
if(x0 == x1) // vertical
{           
    return (y0 < y1) ? EdgeType.RIGHT : 
           (y0 > y1) ? EdgeType.LEFT : 
                       EdgeType.EMPTY;
}
else if(y0 == y1) // horizontal
{
    return (x0 < x1) ? EdgeType.BOTTOM : 
           (x0 > x1) ? EdgeType.TOP : 
                       EdgeType.EMPTY;
}
else
{
    throw new IllegalArgumentException("Edge not orthogonal");
}
}

Regarding your first question, there are a number of ways to find the orientation of a polygon. See the discussion on SO

here.As for comparing the points in a polygon, you can do something like the below:

This will compare each point with the next, including comparing the last point with the first to 'close the loop'. If this isn't needed, you can do a small change to stop as soon as the last point is reached:

Answer 1

这是我可以用来测试组成两个点的边缘是北边、西边、东边还是南边的代码。

enum Orientation {CW, CCW}

public Orientation orientation(List<Point2D> points)
{
    int minIdx = 0;
    for(int i=1; i<points.size(); i++)
        if(pointOrder(points.get(i), points.get(minIdx)) <= 0) minIdx = i;

    int nextIdx = (minIdx+1) % points.size();       
    if(points.get(nextIdx).getY() == points.get(minIdx).getY()) 
        return Orientation.CCW;
    else
        return Orientation.CW;
}

public int pointOrder(Point2D p1, Point2D p2)
{
    if(p1.getY() < p2.getY()) return -1;
    else if(p1.getY() > p2.getY()) return 1;
    else if(p1.getX() < p2.getX()) return -1;
    else if(p1.getX() > p2.getX()) return 1;
    else return 0;
}

我有两个顾虑，没有找到解决方案。

for(int i=0, j=points.size()-1; i<points.size(); j=i++)
{
    EdgeType edgeType = orthoEdgeTypeCCW(points.get(j), points.get(i));
    System.out.format("%s -> %s : %s%n", points.get(j), points.get(i), edgeType);
}

第一...

public EdgeType orthoEdgeTypeCCW(Point2D p1, Point2D p2)
{
    if(p1.getX() == p2.getX()) // vertical
    {           
        return (p1.getY() < p2.getY()) ? EdgeType.RIGHT : 
               (p1.getY() > p2.getY()) ? EdgeType.LEFT : 
                                         EdgeType.EMPTY;
    }
    else if(p1.getY() == p2.getY()) // horizontal
    {
        return (p1.getX() < p2.getX()) ? EdgeType.BOTTOM : 
               (p1.getX() > p2.getX()) ? EdgeType.TOP : 
                                         EdgeType.EMPTY;
    }
    else
    {
        throw new IllegalArgumentException("Edge not orthogonal");
    }
}

我想测试顶点是顺时针还是逆时针排序。因此，我必须修改边缘类型的代码。

第二种

Answer 2

我有一个XML--定义多边形边缘的xy坐标（顶点）列表。我读取这个文件并将顶点保存在ArrayList中。现在，我想在完成的ArrayList上迭代，并 ...

List<Point2D.Float> points = new ArrayList<>(); //your initial set of points
for (int i = 0; i < points.size(); i++) {
    Point2D.Float current = points.get(i);
    Point2D.Float next = points.get((i + 1) % points.size());
    //do your comparison between the two points here
}

对于一个没有自交点的简单正交多边形，你可以确定它的方向（CW）。