凸边界搜索

对于任意给定的离散点搜索其边界，主要通过判断边界类型然后指定相应的搜索方式。一般边界主要分为凸边界和既有凸边界又有凹边界两种类型。如下图所示：

 

对于不同类型的边界有不同的计算算法搜索点，在搜索边界时，现约定统一采用逆时针方向搜索。如现已经存在边界AC，需要搜索下一条边界AB，如下图所示：

添加一个按钮，设置其Name和Text属性都为“凸边界搜索”。由于在搜索到边界时需要添加新的对象，所以采用ArrayList类型，需要添加引用“using System.Collections;”

同时定义类Edge用于保存该边界的起点与终点，如下：

        public class Edge

        {

            public int Start;//边的起点

            public int End;//边的终点

        }

在全局变量中添加定义“private ArrayList arrayEdges = new ArrayList();”用于定义边界数组。

为“凸边界搜索”按钮的Click事件添加代码如下：

        private void 凸边界搜索_Click(object sender, EventArgs e)

        {

            arrayEdges.Clear();

            Microsoft.VisualBasic.Interaction.AppActivate(AcadApp.Caption);

            AcadSelectionSet mySelectionSet;

            mySelectionSet = AcadDoc.SelectionSets.Add("NewSelectionSet001");

            Int16[] FilterType = new Int16[1];

            object[] FilterData = new object[1];

            FilterType[0] = 0;

            FilterData[0] = "POINT";

            mySelectionSet.SelectOnScreen(FilterType, FilterData);

            double[] arrPoints = new double[3 * mySelectionSet.Count];

            int count = 0;

            foreach (AcadObject acadObj in mySelectionSet)

            {

                if (acadObj.ObjectName == "AcDbPoint")

                {

                    count++;

                    double[] PointCoord;

                    PointCoord = (Double[])(((AcadPoint)acadObj).Coordinates);

                    arrPoints[3 * count - 3] = PointCoord[0];

                    arrPoints[3 * count - 2] = PointCoord[1];

                    arrPoints[3 * count - 1] = PointCoord[2];

                }

            }

            AcadDoc.SelectionSets.Item("NewSelectionSet001").Delete();

 

            //获取点集外围边界           

            int i, StartIndex=0, AIndex, BIndex, pointCount = arrPoints.Length / 3;

 

            for (i = 1; i < pointCount; i++) //寻找X值最小的点号

            {

                if (arrPoints[3 * i] < arrPoints[3 * StartIndex])

                {

                    StartIndex = i;

                }

            }

            Edge edge = new Edge();

            edge.Start = StartIndex;

            BIndex = StartIndex - 1;

            AIndex = StartIndex;

            double[] vector1 = new double[2], vector2 = new double[2];

            vector1[0] = 0; vector1[1] = 100;

            double vector1Length, vector2Length, angleTemp, angleMax, lengthMin, vectorDirect;

            angleMax = 0;

            while (BIndex != StartIndex)

            {

                vector1Length = Math.Sqrt(vector1[0] * vector1[0] + vector1[1] * vector1[1]);

                lengthMin = 300;

                for (i = 0; i < pointCount; i++)//找边界

                {

                    if (i != edge.Start)

                    {

                        vector2[0] = arrPoints[3 * i] - arrPoints[3 * AIndex];

                        vector2[1] = arrPoints[3 * i + 1] - arrPoints[3 * AIndex + 1];

                        vector2Length = Math.Sqrt(vector2[0] * vector2[0] + vector2[1] * vector2[1]);

                        angleTemp = Math.Acos((vector1[0] * vector2[0] + vector1[1] * vector2[1]) / (vector1Length * vector2Length));

                        vectorDirect = vector1[0] * vector2[1] - vector1[1] * vector2[0];

                        if (angleTemp > angleMax && vectorDirect<0)

                        {

                            angleMax = angleTemp;

                            edge.End = i;

                            lengthMin = vector2Length;

                        }

                        else if (angleTemp == angleMax && vector2Length < lengthMin)

                        {

                            edge.End = i;

                            lengthMin = vector2Length;

                        }

                    }

                }

                arrayEdges.Add(edge);

                BIndex = edge.End;

 

                edge = new Edge();

                edge.Start = BIndex;

              

                vector1[0] = arrPoints[3 * AIndex] - arrPoints[3 * BIndex];

                vector1[1] = arrPoints[3 * AIndex + 1] - arrPoints[3 * BIndex + 1];

                angleMax = 0;

                AIndex = BIndex;               

            }

 

            //绘制边界

            double[] lineCoords = new double[3*(arrayEdges.Count+1)];

            Edge[] edges = new Edge[arrayEdges.Count];

            arrayEdges.CopyTo(edges);

            for(i=0;i<arrayEdges.Count;i++)

            {

                double[] p1=new double[3];

                p1[0] = arrPoints[3 * edges[i].Start];

                p1[1] = arrPoints[3 * edges[i].Start+1];

                p1[2] = arrPoints[3 * edges[i].Start+2];

                lineCoords[3 * i] = arrPoints[3 * edges[i].Start];

                lineCoords[3 * i + 1] = arrPoints[3 * edges[i].Start + 1];

                lineCoords[3 * i + 2] = arrPoints[3 * edges[i].Start + 2];

            }

            lineCoords[3 * arrayEdges.Count - 3] = arrPoints[3 * edges[arrayEdges.Count - 1].Start];

            lineCoords[3 * arrayEdges.Count - 2] = arrPoints[3 * edges[arrayEdges.Count - 1].Start + 1];

            lineCoords[3 * arrayEdges.Count - 1] = arrPoints[3 * edges[arrayEdges.Count - 1].Start + 2];

            lineCoords[3 * arrayEdges.Count] = arrPoints[3 * edges[arrayEdges.Count-1].End];

            lineCoords[3 * arrayEdges.Count+1] = arrPoints[3 * edges[arrayEdges.Count-1].End + 1];

            lineCoords[3 * arrayEdges.Count+2] = arrPoints[3 * edges[arrayEdges.Count - 1].End + 2];

            AcadDoc.ModelSpace.Add3DPoly(lineCoords);

        }

运行程序，其结果如下图所示：