007集—— 自动获取图形的外边界（外轮廓）（CAD—C#二次开发入门）
本文只适用于闭合多段线组成的图像，其他情况（圆、弧、椭圆、未封闭line）暂不支持。
效果如下图所示：
原始图：
代码运行后图：
附代码：
public class 外轮廓{Database db = HostApplicationServices.WorkingDatabase;[CommandMethod("xx")]public void Demo(){try{//ObjectId obj = db.GetCenterPl();// return;// List<DBText> dbtext = db.SelectEntities<DBText>();// return;// db.GetEntities(out List<Curve> curve, "aa");// return;if (!db.GetEntities(out List<Curve> curve, "框选识别外轮廓的图像"))return;List<Line> lines = new List<Line>();foreach (var item in curve){if (item is Line) lines.Add(item as Line);else if (item is Polyline pl){List<Curve> cus = PmPolyLineMethod.ExplodePolyLine(pl);foreach (var cu in cus){if (cu is Line) lines.Add(cu as Line);}}}//lines.ForEach(line => line.ColorIndex = 1);//foreach (var item in lines)//{// db.AddEntityToModeSpace(item);//}//return;Dictionary<Line, List<Point3d>> pointsOnLine = new Dictionary<Line, List<Point3d>>();foreach (var item in lines){pointsOnLine.Add(item, new List<Point3d>());}for (int i = 0; i < lines.Count - 1; i++){for (int j = i + 1; j < lines.Count; j++){Point3dCollection pos = new Point3dCollection();lines[i].IntersectWith(lines[j], Intersect.OnBothOperands, pos, IntPtr.Zero, IntPtr.Zero);if (pos.Count > 0){foreach (Point3d item in pos){pointsOnLine[lines[i]].Add(item);pointsOnLine[lines[j]].Add(item);}}}}lines.Clear();foreach (var item in pointsOnLine){Line line = item.Key;List<Point3d> points = item.Value;if (points.Count == 0){lines.Add(line);}else{if (points.Count > 1){points = points.OrderBy(x => line.GetParameterAtPoint(x)).ToList();//点排序}Point3dCollection pos = new Point3dCollection();points.ForEach(x => pos.Add(x));//点集合加点DBObjectCollection dbs = line.GetSplitCurves(pos);//打断线foreach (var dbobject in dbs){if (dbobject is Line){lines.Add(dbobject as Line);//最终线段list}}}}//lines.ForEach(line => line.ColorIndex = 1);//lines.ForEach(line => db.AddEntityToModeSpace(line));//return;if (!PmPolyLineMethod.GetPoint(out Point3d point, "请选择外面一点")) return;Line firstLine = lines.OrderBy(x => x.GetClosestPointTo(point, false).DistanceTo(point)).First();//firstLine.ColorIndex = 1;//db.AddEntityToModeSpace(firstLine);//return;lines.Remove(firstLine);Polyline polyline = new Polyline();polyline.AddVertexAt(0, firstLine.StartPoint.Convert2d(new Plane()), 0, 0, 0);polyline.AddVertexAt(1, firstLine.EndPoint.Convert2d(new Plane()), 0, 0, 0);Vector3d v1 = firstLine.StartPoint - point;Vector3d v2 = firstLine.EndPoint - point;if (v1.CrossProduct(v2).Z > 0) polyline.ReverseCurve();//polyline.ColorIndex = 1;//db.AddEntityToModeSpace(polyline);//return;while (true){List<Line> tmps = new List<Line>();foreach (var item in lines){if (item.StartPoint == polyline.EndPoint){tmps.Add(item);}else if (item.EndPoint == polyline.EndPoint){item.ReverseCurve();tmps.Add(item);}}if (tmps.Count == 0) break;Vector3d vector = -polyline.GetFirstDerivative(polyline.EndPoint);//顺时针double maxAngle = 0;Line bigLine = new Line();foreach (var item in tmps)//{double angle = vector.GetAngleTo(item.Delta, -Vector3d.ZAxis);if (angle > maxAngle){maxAngle = angle;bigLine = item;}}polyline.JoinEntity(bigLine);lines.Remove(bigLine);if (polyline.EndPoint == polyline.StartPoint) break;}polyline.ColorIndex = 1;db.AddEntityToModeSpace(polyline);return;}catch (System.Exception){throw;}}}说明：db.GetEntities 等函数为本博封装函数。获取联系下方↓↓↓