我想确定一个多边形,并实现一个算法来检查一个点是否在多边形内部或外部。
有没有人知道是否有任何类似算法的可用示例?
我想确定一个多边形,并实现一个算法来检查一个点是否在多边形内部或外部。
有没有人知道是否有任何类似算法的可用示例?
C# 代码
bool IsPointInPolygon(List<Loc> poly, Loc point)
{
int i, j;
bool c = false;
for (i = 0, j = poly.Count - 1; i < poly.Count; j = i++)
{
if ((((poly[i].Lt <= point.Lt) && (point.Lt < poly[j].Lt))
|| ((poly[j].Lt <= point.Lt) && (point.Lt < poly[i].Lt)))
&& (point.Lg < (poly[j].Lg - poly[i].Lg) * (point.Lt - poly[i].Lt)
/ (poly[j].Lt - poly[i].Lt) + poly[i].Lg))
{
c = !c;
}
}
return c;
}
位置(Location)类
public class Loc
{
private double lt;
private double lg;
public double Lg
{
get { return lg; }
set { lg = value; }
}
public double Lt
{
get { return lt; }
set { lt = value; }
}
public Loc(double lt, double lg)
{
this.lt = lt;
this.lg = lg;
}
}
在搜索网络和尝试不同的实现并将它们从C++移植到C#后,我终于让我的代码变得正确:
public static bool PointInPolygon(LatLong p, List<LatLong> poly)
{
int n = poly.Count();
poly.Add(new LatLong { Lat = poly[0].Lat, Lon = poly[0].Lon });
LatLong[] v = poly.ToArray();
int wn = 0; // the winding number counter
// loop through all edges of the polygon
for (int i = 0; i < n; i++)
{ // edge from V[i] to V[i+1]
if (v[i].Lat <= p.Lat)
{ // start y <= P.y
if (v[i + 1].Lat > p.Lat) // an upward crossing
if (isLeft(v[i], v[i + 1], p) > 0) // P left of edge
++wn; // have a valid up intersect
}
else
{ // start y > P.y (no test needed)
if (v[i + 1].Lat <= p.Lat) // a downward crossing
if (isLeft(v[i], v[i + 1], p) < 0) // P right of edge
--wn; // have a valid down intersect
}
}
if (wn != 0)
return true;
else
return false;
}
private static int isLeft(LatLong P0, LatLong P1, LatLong P2)
{
double calc = ((P1.Lon - P0.Lon) * (P2.Lat - P0.Lat)
- (P2.Lon - P0.Lon) * (P1.Lat - P0.Lat));
if (calc > 0)
return 1;
else if (calc < 0)
return -1;
else
return 0;
}
isLeft函数给我带来了四舍五入的问题,而我却花费了数小时才意识到自己转换错误,因此请原谅我在该函数末尾使用的愚蠢if语句块。
顺便说一下,这是原始代码和文章: http://softsurfer.com/Archive/algorithm_0103/algorithm_0103.htm
int pnpoly(int npol, float *xp, float *yp, float x, float y)
{
int i, j, c = 0;
for (i = 0, j = npol-1; i < npol; j = i++) {
if ((((yp[i] <= y) && (y < yp[j])) ||
((yp[j] <= y) && (y < yp[i]))) &&
(x < (xp[j] - xp[i]) * (y - yp[i]) / (yp[j] - yp[i]) + xp[i]))
c = !c;
}
return c;
}
这是一个关于asp.Net C#的完整解决方案,你可以在这里查看完整细节。你可以了解如何使用纬度和经度来判断点(lat,lon)是否在多边形内部或外部。
文章参考链接private static bool checkPointExistsInGeofencePolygon(string latlnglist, string lat, string lng) {
List<Loc> objList = new List<Loc>();
// sample string should be like this strlatlng = "39.11495,-76.873259|39.114588,-76.872808|39.112921,-76.870373|";
string[] arr = latlnglist.Split('|');
for (int i = 0; i <= arr.Length - 1; i++)
{
string latlng = arr[i];
string[] arrlatlng = latlng.Split(',');
Loc er = new Loc(Convert.ToDouble(arrlatlng[0]), Convert.ToDouble(arrlatlng[1]));
objList.Add(er);
}
Loc pt = new Loc(Convert.ToDouble(lat), Convert.ToDouble(lng));
if (IsPointInPolygon(objList, pt) == true)
{
return true;
}
else
{
return false;
}
}
private static bool IsPointInPolygon(List<Loc> poly, Loc point)
{
int i, j;
bool c = false;
for (i = 0, j = poly.Count - 1; i < poly.Count; j = i++)
{
if ((((poly[i].Lt <= point.Lt) && (point.Lt < poly[j].Lt)) |
((poly[j].Lt <= point.Lt) && (point.Lt < poly[i].Lt))) &&
(point.Lg < (poly[j].Lg - poly[i].Lg) * (point.Lt - poly[i].Lt) / (poly[j].Lt - poly[i].Lt) + poly[i].Lg))
c = !c;
}
return c;
}
仅提醒一下(由于不能评论,我使用答案),如果您想要在地理围栏中使用点-多边形算法,则需要更改算法以适用于球面坐标系。-180经度与180经度相同,在这种情况下,点-多边形将会失败。
关于kobers的回答,我通过更易读的干净代码解决了问题,并更改了跨越日期边界的经度:
public bool IsPointInPolygon(List<PointPosition> polygon, double latitude, double longitude)
{
bool isInIntersection = false;
int actualPointIndex = 0;
int pointIndexBeforeActual = polygon.Count - 1;
var offset = calculateLonOffsetFromDateLine(polygon);
longitude = longitude < 0.0 ? longitude + offset : longitude;
foreach (var actualPointPosition in polygon)
{
var p1Lat = actualPointPosition.Latitude;
var p1Lon = actualPointPosition.Longitude;
var p0Lat = polygon[pointIndexBeforeActual].Latitude;
var p0Lon = polygon[pointIndexBeforeActual].Longitude;
if (p1Lon < 0.0) p1Lon += offset;
if (p0Lon < 0.0) p0Lon += offset;
// Jordan curve theorem - odd even rule algorithm
if (isPointLatitudeBetweenPolyLine(p0Lat, p1Lat, latitude)
&& isPointRightFromPolyLine(p0Lat, p0Lon, p1Lat, p1Lon, latitude, longitude))
{
isInIntersection = !isInIntersection;
}
pointIndexBeforeActual = actualPointIndex;
actualPointIndex++;
}
return isInIntersection;
}
private double calculateLonOffsetFromDateLine(List<PointPosition> polygon)
{
double offset = 0.0;
var maxLonPoly = polygon.Max(x => x.Longitude);
var minLonPoly = polygon.Min(x => x.Longitude);
if (Math.Abs(minLonPoly - maxLonPoly) > 180)
{
offset = 360.0;
}
return offset;
}
private bool isPointLatitudeBetweenPolyLine(double polyLinePoint1Lat, double polyLinePoint2Lat, double poiLat)
{
return polyLinePoint2Lat <= poiLat && poiLat < polyLinePoint1Lat || polyLinePoint1Lat <= poiLat && poiLat < polyLinePoint2Lat;
}
private bool isPointRightFromPolyLine(double polyLinePoint1Lat, double polyLinePoint1Lon, double polyLinePoint2Lat, double polyLinePoint2Lon, double poiLat, double poiLon)
{
// lon <(lon1-lon2)*(latp-lat2)/(lat1-lat2)+lon2
return poiLon < (polyLinePoint1Lon - polyLinePoint2Lon) * (poiLat - polyLinePoint2Lat) / (polyLinePoint1Lat - polyLinePoint2Lat) + polyLinePoint2Lon;
}
多边形被定义为点对A、B、C……A的顺序列表。 没有边A-B、B-C……与其他边相交
确定框Xmin、Xmax、Ymin、Ymax
情况1 测试点P在框外
情况2 测试点P在框内:
确定框的“直径”D{[Xmin,Ymin] - [Xmax,Ymax]}(并添加一些额外的内容以避免可能与D在一侧混淆)
确定所有边的梯度M
找到一个梯度Mt,它与所有梯度M最不同
测试线从P开始,以Mt梯度和距离D运行。
将交点计数设置为零
对于每个边A-B、B-C,测试P-D与其起点到但不包括其终点的边的交点。如有必要,增加交点计数。请注意,从P到交点的零距离表示P在一条边上
奇数计数表示P在多边形内