To calculate Smoothing Groups, first, the vertex and face normals are calculated, which are then used to look at all the faces that connect to a particular face. By calculating the angle between the normals, we can then determine if an edge is hard or soft (similar to the Soft/Hard Edges tool in Maya). Below, the image on the left we would consider a soft edge, while the image on the right, a hard edge. This is because the angle between the two normals in the image on the left is smaller than that of the angle of the two normals in the image on the right.