can be a source of confusion when linking to AutoCAD, AutoCAD Architecture, or Revit drawing files. In 3ds Max Design, every face has a front and a back, corresponding to the inside or outside surface of a solid object. In a cube, for example, there is seldom the need to view the inside surface of any of the six squares that make up the cube. So for many viewing and rendering operations, 3ds Max Design ignores a face if it's facing away (that is, if its face normal is directed away) from a point of view.
When you create objects in AutoCAD, AutoCAD Architecture, or Revit, 3ds Max Design generally understands which way faces should be oriented and manages face normals accordingly. However, occasionally you may encounter linked drawing geometry that displays correctly in AutoCAD, AutoCAD Architecture, or Revit, but doesn't strictly respect face-normal conventions. This can make it appear as though elements visible in the drawing file are missing or appear “inside-out” in 3ds Max Design.
If you experience a high volume of face normal problems in a particular file, verify that the Weld switch is on, and then reload the drawing. Weld forces nearby faces to share edges and vertices. Welding can still result in groups of face normals that are flipped in 3ds Max Design, in which case, turn on Unify Normals as well.
Two-dimensional elements in drawing files, such as lines, polylines, circles, and arcs, are represented as splines in 3ds Max Design. These splines carry much more information at each vertex than typical AutoCAD 2D structures. Since some drawing files contain large quantities of 2D data, exercise caution when linking files containing a high number of discrete line segments. There are two ways these elements can be left out of your 3ds Max Design scene:
3D Solids objects that you link from a drawing file into 3ds Max Design are tessellated; that is, turned into mesh objects with faces. The fineness of the tessellation is controlled by the on the File Link Settings: DWG Files dialog. A high value results in coarser tessellation. 3ds Max Design uses less memory in the scene, but poor approximations of curved surfaces could result. For acceptable performance, keep this value as high as possible.
Splines are not rendered in 3ds Max Design unless they have rendering parameters applied. Normally, you have to collapse a shape to an editable spline object in order to apply rendering parameters; however, this is not possible with spline objects from AutoCAD.
In Revit, a DWG, DXF or RVT file can be linked to the project. This kind of link is called a . When the project is exported to a DWG file, this type of link is represented in the exported drawing as an external referenced drawing. In this case, more than one drawing file may be created, with one referencing the other(s).
An xref file that contains a sequence of nested references that refers back to the xref file is considered a circular reference. 3ds Max Design resolves xrefs until it detects a circular reference. For example, if you have the circular reference A|B|C|A, 3ds Max Design detects and breaks the circularity between C and A. This is consistent with the way AutoCAD and AutoCAD Architecture handle circular xref dependencies.
If you want to clone actively linked objects, you should only use the Copy option. Creating references or instances of actively linked objects is not recommended, as reliability issues can arise when the instanced or referenced object is deleted in the linked file.
When you copy actively linked objects, linked through the , the copies are automatically converted to editable mesh or editable spline objects. If your selection contains several objects which instance another object, the resulting copies also instance the same object.
If you use an actively linked object as part of a compound object, you should always choose Copy when you specify how the linked object is transferred to the compound object. Choosing Reference or Instance can cause instability in 3ds Max Design.
Actively linked objects should not be attached to editable objects, as this introduces instability to 3ds Max Design. Instead, make a copy of the actively linked object, and attach the clone to the editable object.
Creating parent-child links between actively linked objects AND 3ds Max Design objects can cause unpredictable results. For this reason, 3ds Max Design does not allow you to link an actively linked object to a 3ds Max Design object. However, you can link a 3ds Max Design object to an actively linked object.