如何在C#中从OpenStreetMap边界关系创建一个或多个多边形？

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Xml;

public class OpenStreetMapPolygonCreator
{
    public List<List<PointF>> CreatePolygonsFromBoundaryRelation(string boundaryRelationXml)
    {
        List<List<PointF>> polygons = new List<List<PointF>>();

        XmlDocument xmlDoc = new XmlDocument();
        xmlDoc.LoadXml(boundaryRelationXml);

        // 解析边界关系数据
        XmlNodeList memberNodes = xmlDoc.SelectNodes("//member[@type='way']");
        foreach (XmlNode memberNode in memberNodes)
        {
            string wayRef = memberNode.Attributes["ref"].Value;
            XmlNode wayNode = xmlDoc.SelectSingleNode($"//way[@id='{wayRef}']");
            if (wayNode != null)
            {
                List<PointF> polygon = new List<PointF>();

                // 提取多边形节点信息
                XmlNodeList ndNodes = wayNode.SelectNodes("nd");
                foreach (XmlNode ndNode in ndNodes)
                {
                    string nodeRef = ndNode.Attributes["ref"].Value;
                    XmlNode node = xmlDoc.SelectSingleNode($"//node[@id='{nodeRef}']");
                    if (node != null)
                    {
                        float lat = float.Parse(node.Attributes["lat"].Value);
                        float lon = float.Parse(node.Attributes["lon"].Value);
                        PointF point = new PointF(lon, lat);
                        polygon.Add(point);
                    }
                }

                polygons.Add(polygon);
            }
        }

        return polygons;
    }
}