Which method is typically used to smooth sharp edges in 3D models?

The method commonly employed to smooth sharp edges in 3D models is the calculation of normals. Normals are vectors that are perpendicular to the surface of a 3D model and they play a crucial role in determining how light interacts with that surface. When the normals are calculated properly, they can create the illusion of a smooth surface, even if the underlying geometry is made up of flat polygons.

By averaging the normals of adjacent faces, the lighting across those faces can appear softer, which effectively reduces the visibility of sharp edges. This technique is essential in rendering, as it enhances the visual quality of models without requiring a significant increase in polygon count.

In contrast, refining edge, smoothing groups, and polygon reduction serve different purposes. Refining edges pertains to improving edge definitions but does not directly involve normals. Smoothing groups connect adjacent polygon faces to create smooth shading transitions, yet this still relies on the underlying normal calculations. Polygon reduction focuses on reducing the complexity of a model by decreasing the number of polygons, which does not directly address sharp edge smoothing but rather aims to optimize model performance and efficiency.