Inverting and Unifying Faces and Normals

Use

3D applications have polygon faces that are either double-sided or single-sided. Single-sided faces are visible on one side and invisible on the other, resulting in higher rendering rates for real-time 3D software. Also, certain applications define “visible” as a face that has points defined in a clockwise order relative to the viewing camera. With others, it is points defined in a counter-clockwise order.

For example, if a model looks “inside-out” when imported, the original application either supported double-sided faces, or faces that were defined to be visible if counter-clockwise.

As there is no way to define which faces are visible when importing models, some faces and/or surface normals may be incorrectly orientated (facing backwards). You can use the Invert tools to reverse the order of the points and “flipping” the direction of the normals on the faces of the model.

If you select one or more objects, only the faces or normals of the selection are reversed. If no objects are selected, all faces or normals of the model are reversed.

Unify Normals

You can use the Unify Normals tool to orient all normals correctly, that is, align them in the same direction. This is helpful when imported geometry is not properly joined, resulting in surface normals being oriented in the wrong direction, and models displaying incorrectly.

You can choose the action for objects with incorrectly aligned normals: select, highlight, or mark as double-sided. If you choose to select objects, you can then use other CADTools tools to correct the selected faces. For example, you could invert the normals.

Activities

Inverting Faces and Normals

  1. Open a 3D file and select the objects for which you want to invert face or normals.

  2. Do one of the following:

    • Click Invert Faces to invert faces only.

    • Click Invert Normals to invert surface normals only.

    • Click Invert Faces and Normals to invert faces and surface normals.

The objects’ faces and normals are inverted.

Unifying Normals

  1. Open a 3D file and click Unify Normals on the CADTools toolbar.

  2. Make your selections as required and click OK.

The objects are selected, highlighted, or marked as double-sided depending on your selection.