DXF files are used to import and export objects to and from AutoCAD (and other programs that support this file format).
Keep the following in mind when you are creating your DXF geometry, and when you are deciding whether to convert by layer, color, or entity:
Entities that are frozen or turned off are ignored.
The successful unification of face normals depends on the welding of coincident vertices. Sometimes, depending upon the precision of the model as it was created in AutoCAD, the vertices may not be close enough to be considered "coincident." They will not be welded, and the faces will not be properly unified. In this case, increase the Weld Threshold value in the Import DXF File dialog.
Converting by layer can result in objects consisting of many elements. In certain cases, some of these elements may have all of their face normals flipped the wrong way. You can detect this in 3D Studio MAX by clearing Backface Cull in the Display panel or by rendering the objects. Use the Normal modifier to correct this.
If you do not want to flip normals, you can either use 2-sided materials, or turn on the Force 2-Sided option in the Render Scene dialog.
If you are loading a large scene containing thousands of entities (such as 3D faces) and have chosen to load an object by entity, the conversion can take a long time. It also produces a huge number of objects to handle in 3D Studio MAX. To avoid this, organize your DXF file so that these kinds of entities are grouped by layer, then make the conversion by layer rather than by entity.
The following controls appear in the Import DXF File dialog.
Derive Objects From: Determines how components in the .dxf file are to be converted into objects.
Layer: Each layer with a unique name is converted into a separate object.
Color: All entities of the same color are converted into a single entity.
Entity: Each entity is converted into a separate object.
Weld Vertices: Welds coincident vertices in the .dxf file into single vertices in the 3D Studio MAX mesh.
Weld Threshold: Determines the size of the area which vertices must occupy to be welded.
Weld: Turns on the Weld Vertices function. In most cases, you should leave this box selected because unwelded objects cannot be correctly unified or smoothed.
Auto-Smooth: Applies smoothing groups to the geometry based on the smoothing angle set by the smooth angle spinner. Edges between faces that have an angle between them that is greater than the specified smoothing angle will appear faceted in the rendered image. Edges between faces that are below the specified angle are smoothed.
Polygon Degrees: Specifies the number of degrees between each vertex any imported curvature that’s converted to a mesh object in 3D Studio MAX. An example might be an extruded pline.
Spline Degrees: Specifies the number of degrees between vertices in an imported curvature that’s converted to a Bezier spline (a shape) in 3D Studio MAX. This could be an arc or a non-extruded pline, for example. Unlike mesh objects, Bezier splines contain their own curvatures, so you don’t need as many vertices. The default setting of 90 degrees is usually adequate.
Remove Double Faces: Removes one of the pair wherever two faces are occupying the same location.
Fill Polylines: Converts closed 2D polylines into mesh objects. Closed, planar, 3D polylines are capped. If the 2D polyline is open, it will be imported as a spline shape.
Unify Normals: Forces the normals of all faces on each object to face the same way (usually out). If, when you render your 3D Studio MAX scene, the face normals are pointing in the wrong direction, use the Normal modifier to flip them. For best results, leave this box selected.