C#+AE 判斷點是否在面內的方法

整體思路：射線法。

①：先判斷點的X和Y坐標和多邊形的Xmin,Xmax,Ymin,Ymax的關系。若超出了這四個值，則一定在多邊形外；

②：若不符合上述條件，則繼續。向左做線段，線段的左頂點的X坐標值一定要小於Xmin。然后判斷線段和多邊形的交點；

若交點為偶數個，則在多邊形外；若交點為奇數個，則點在多邊形內；

③：因為最后取的交點是按照Ipolyline和多邊形Polygon作得拓撲關系的交集，交集是IGeometry對象，其向IgeometryCollection對象跳轉，最后得到一個點擊IpointCollection，根據PointCount屬性可得到相交點的個數。

 

 

得到最小X坐標值的函數：

    public double getXMinValue(IPolygon nPolygon)
        {
            IPolygon sPolygon;
            sPolygon = nPolygon;
            IPointCollection pPointCollection;
            pPointCollection = sPolygon as IPointCollection;

            int n = pPointCollection.PointCount;
            double[] coordX = new double[n];
         
            for (int i = 0; i < n; i++)
            {
                IPoint point = pPointCollection.get_Point(i);
                coordX[i] = point.X;
            }
            //對數組進行從小到大排序
            System.Array.Sort(coordX);        

            Xmin = coordX[0];           
            return Xmin;
        }

向左畫射線並得到交點個數的代碼：

try
                        {
 
                            ILine newLine = new LineClass();

                            IPoint toPoint = new PointClass();
                            toPoint.PutCoords(getXMinValue(pPolygon) - 20.0000000000000, pPoint.Y);

                            newLine.PutCoords(pPoint, toPoint);//給新的直線賦予起始坐標

                            //苗師兄想法
                            IPolyline l = new PolylineClass();
                            l.FromPoint = pPoint;
                            l.ToPoint = toPoint;

                            IGeometryCollection pPolyline = new PolylineClass();
                            ISegmentCollection pPath;
                            pPath = new PathClass();
                            object missing1 = Type.Missing;
                            object missing2 = Type.Missing;

                            pPath.AddSegment(newLine as ISegment, ref missing1, ref missing2);
                            pPolyline.AddGeometry(pPath as IGeometry, ref missing1, ref missing2);

                            IElement element = DrawLineSymbol(pPolyline as IGeometry, pColor);
                            pGraph.AddElement(element, 0);
                            pActiveView.PartialRefresh(esriViewDrawPhase.esriViewGraphics, null, null);

                        
                            ITopologicalOperator pTopo = pPolygon as ITopologicalOperator;//pPolygon多邊形
                            IGeometryCollection pGeoCol = pTopo.Intersect((IGeometry)l, esriGeometryDimension.esriGeometry0Dimension) as IGeometryCollection; //執行到這一句有問題；
                            IPointCollection pPointCol = pGeoCol as IPointCollection;
                            if ((pPointCol.PointCount) % 2 == 0)
                            {
                                MessageBox.Show("射線和多邊形的交點個數為："+pPointCol.PointCount.ToString()+",點在多邊形外。");
                            }
                            else
                            {
                                MessageBox.Show("射線和多邊形的交點個數為："+pPointCol.PointCount.ToString()+",點在多邊形內。");
                            }
                          

                        }
                        catch (Exception ex)
                        {
                            MessageBox.Show(ex.Message);
                        }

 

本文是按照Polygon對象考慮的面，所以並未考慮重疊面的問題。