获取Civil 3D 三角网曲面TinSurface中每个小三角形的法向量

Civil 3D 2012以后版本提供的曲面的.net API,通过.net API可以获得TinSurface的所有三角形(TinSurfaceTriangle)信息，包含顶点(Vertex)和边(Edge)。但TinSurfaceTriangle对象没有提供表示该三角形法向量（normal）的函数方法，下面自己来实现一个。思路的利用小三角形的顶点信息构建一个AutoCAD 的plane实体，进而获取法向量：

        Vector3d GetNormal(TinSurfaceTriangle triangle)
        {
            Point3d point1 = triangle.Vertex1.Location;
            Point3d point2 = triangle.Vertex2.Location;
            Point3d point3 = triangle.Vertex3.Location;
 
            Vector3d normal;
            using (Plane plan = new Plane(
                point1, 
                point1.GetVectorTo(point2), 
                point1.GetVectorTo(point3)))
            {
                normal = plan.Normal.GetNormal();
            };
 
            return normal;
        }
 另一种方法：

        Vector3d GetNormal2(TinSurfaceTriangle triangle)
        {
            Point3d point1 = triangle.Vertex1.Location;
            Point3d point2 = triangle.Vertex2.Location;
            Point3d point3 = triangle.Vertex3.Location;
 
            Vector3d v1 = point1.GetVectorTo(point2).GetNormal();
            Vector3d v2 = point1.GetVectorTo(point3).GetNormal();
 
            Vector3d normal = v2.CrossProduct(v1).GetNormal();
 
            return normal;
        }

下面是对曲面操作的一个测试函数：

        [CommandMethod("PrintSurfaceInfo")]
        public void PrintSurfaceInfo()
        {
           
            ObjectId surfaceId = ObjectId.Null;
 
            do
            {
                surfaceId = this.PromptForTinSurface();
            }
            while (surfaceId == ObjectId.Null);
 
             Database db = CurrentEditor.Document.Database;
            using (Transaction trans = db.TransactionManager.StartTransaction())
            {
                TinSurface surface = trans.GetObject(surfaceId, OpenMode.ForRead) as TinSurface;
 
                int triCount = surface.Triangles.Count;
 
                StringBuilder msg = new StringBuilder();
                msg.Append("\nSurface triangle count: " + triCount.ToString());
                foreach (TinSurfaceTriangle tri in surface.Triangles)
                {
                    msg.Append(GetTriangleInfo(tri));
                }
 
                CurrentEditor.WriteMessage(msg.ToString());
            }
        }
 
 
        string GetTriangleInfo(TinSurfaceTriangle triangle)
        {
            StringBuilder sb = new StringBuilder();
            sb.Append("\n");
            sb.Append("\nPoint1 : " + triangle.Vertex1.Location.ToString());
            sb.Append("\nPoint2 : " + triangle.Vertex2.Location.ToString());
            sb.Append("\nPoint3 : " + triangle.Vertex3.Location.ToString());
            sb.Append("\nNormal : " + GetNormal2(triangle).ToString());
 
            return sb.ToString();
        }
 
        Vector3d GetNormal(TinSurfaceTriangle triangle)
        {
            Point3d point1 = triangle.Vertex1.Location;
            Point3d point2 = triangle.Vertex2.Location;
            Point3d point3 = triangle.Vertex3.Location;
 
            Vector3d normal;
            using (Plane plan = new Plane(
                point1, 
                point2.GetVectorTo(point1), 
                point3.GetVectorTo(point1)))
            {
                normal = plan.Normal;
            };
 
            return normal;
        }
 
        ObjectId PromptForTinSurface()
        {
            string promptMsg = "\nSelect a Tin Surface";
            string rejectMsg = "\n The surface you selected is not Tin Surface";
            PromptEntityOptions opts = new PromptEntityOptions(promptMsg);
            opts.SetRejectMessage(rejectMsg);
            opts.AddAllowedClass(typeof(TinSurface), false);
            PromptEntityResult entRes = CurrentEditor.GetEntity(opts);
            if (entRes.Status == PromptStatus.OK)
            {
                return entRes.ObjectId;
            }
            return ObjectId.Null;
        }
 
        CivilDocument CivilDoc {
            get{
                return CivilApplication.ActiveDocument;
            }
        }
 
        Editor CurrentEditor {
            get{
                return Application.DocumentManager.MdiActiveDocument.Editor;
            }
        }