通过给定点和两已知直线做垂线段

 这个是在objectArx网站上看到别人提的问题，其实一开始我也不会，不过看了别人的提示之后，也就会了，废话少说，上代码：

[CommandMethod("test")] public void test() {     Document doc = Application.DocumentManager.MdiActiveDocument;     Database db = doc.Database;     Transaction trans = db.TransactionManager.StartTransaction();     BlockTable bt = trans.GetObject(db.BlockTableId, OpenMode.ForRead) as BlockTable;     BlockTableRecord btr = trans.GetObject(bt[BlockTableRecord.ModelSpace], OpenMode.ForWrite) as BlockTableRecord;     Line l1 = new Line(new Point3d(100, 400, 0), new Point3d(200, 600, 0));     Line l2 = new Line(new Point3d(150, 400, 0), new Point3d(300, 700, 0));     l1.ColorIndex = 2;     l2.ColorIndex = 2;     Point3d p1, p2;     p1 = l1.GetClosestPointTo(new Point3d(500, 500, 0), true);     p2 = l2.GetClosestPointTo(p1, true);     Line c = new Line(p1,p2);     c.ColorIndex = 1;     btr.AppendEntity(l1);     trans.AddNewlyCreatedDBObject(l1, true);     btr.AppendEntity(l2);     trans.AddNewlyCreatedDBObject(l2, true);     btr.AppendEntity(c);     trans.AddNewlyCreatedDBObject(c, true);     trans.Commit();     trans.Dispose(); }

 运行后效果如下，红色线段即是：