程序实现曲面切割

下面这段代码来自一个客户，实现用一个曲面切割另外一个，比如用一块铁板把一个两头有盖的汽油桶切成两个开口的桶。原理很简单，就是利用了AcDbSurface的SliceBySurface方法：

切割前：

切割后，为了看得清楚，把无盖桶移动了一下：

代码：

        [CommandMethod("TestSliceSurface")]
        public void TestSliceSurface()
        {
            Document doc = Autodesk.AutoCAD.ApplicationServices.Application.DocumentManager.MdiActiveDocument;
            var ed = doc.Editor;

            using (DocumentLock docLock = doc.LockDocument())
            {
                Database db = doc.Database;
                using (Transaction ts = db.TransactionManager.StartTransaction())
                {
                    BlockTableRecord btr = ts.GetObject(db.CurrentSpaceId, OpenMode.ForWrite) as BlockTableRecord;
                    var peo1 = new PromptEntityOptions("\nSelect first surface");
                    peo1.SetRejectMessage("\nMust be a surface.");
                    peo1.AddAllowedClass(typeof(AcDb.Surface), false);

                    var per1 = ed.GetEntity(peo1);
                    if (per1.Status != PromptStatus.OK)
                        return;

                    var obj1 = ts.GetObject(per1.ObjectId, OpenMode.ForWrite);
                    var surf1 = obj1 as AcDb.Surface;
                    if (surf1 == null)
                    {

                        ed.WriteMessage("\nFirst object must be a surface.");
                        return;
                    }
                    
                    var peo2 = new PromptEntityOptions("\nSelect second surface");
                    peo2.SetRejectMessage("\nMust be a surface.");
                    peo2.AddAllowedClass(typeof(AcDb.Surface), false);

                    var per2 = ed.GetEntity(peo2);
                    if (per2.Status != PromptStatus.OK)
                        return;

                    var obj2 = ts.GetObject(per2.ObjectId, OpenMode.ForWrite);
                    var surf2 = obj2 as AcDb.Surface;
                    if (surf2 == null)
                    {

                        ed.WriteMessage("\nSecond object must be a surface.");
                        return;
                    }

                    SurfaceSliceResults ss = surf1.SliceBySurface(surf2);

                    btr.AppendEntity(ss.NegativeHalfSurface);
                    ts.AddNewlyCreatedDBObject(ss.NegativeHalfSurface, true);

                    ts.Commit();
                    ts.Dispose();

                }
                docLock.Dispose();
                
            }
            
        }