中文摘要：

分析了经典D2形状描述符的原理。针对经典D2描述符的不足，提出利用三维模型面片的法向量方向分布特征构造一个具有旋转不变性的形状描述符N2，并用一种相关反馈算法将N2描述符和D2描述符组合起来以获得更好的检索准确度。该方法充分利用了机械模型自身的特点，实验表明其检索准确性显著高于经典D2描述符，同时具有良好的计算效率。

英文摘要：

The traditional D2 shape desriptor was discussed. To enhance the performance of D2, then an shape descriptor called N2 was proposed. N2 was built on the feature of the distrbution of model face normals. A relevant feedback algorithm was introduced to combine the N2 and D2 to achieve higher retrieval precision. The proposed method considered the characteristics of mechanical part models,and experitments show that the proposed method outperforms D2 in retrieval precision significantly with a minor increase of computational time.