1. A method for side detection of a 3D undetailed ear impression, comprising: receiving a 3D undetailed ear impression; defining a local coordinate system of the 3D undetailed ear impression based on side independent features of the 3D undetailed ear impression; detecting a skeleton of the 3D undetailed ear impression, wherein said skeleton is a center spline of the 3D undetailed ear impression; and determining whether the 3D undetailed ear impression is a left or right ear impression based on said skeleton and said local coordinate system of the 3D undetailed ear impression.