For bilateral symmetry objects , the techniques on symmetry - point detection and symmetry - axis extraction are presented based on harmonic conjugation relationship . for rotated symmetry objects , the techniques on rotated units description and rotated symmetry center extraction are presented based on center invariants of objects . further more , by using 3d invariants and 2d projective transformation , an approach to recover shape from part symmetry objects is realized on some conditions ( 3 )深入分析了2d对称性目标透视成像的几何特点，将共点四线交比用于目标轮廓上的关键点的特性描述中；利用调和共轭关系，提出了一种针对左右对称型目标的对称点检测和对称轴提取的算法；利用交比关系构造了目标的形心不变量，提出了一种针对旋转对称型目标的旋转对称单元判定、旋转中心提取的算法；进一步利用3d不变量和2d射影变换，实现了一定条件下的对称性目标的形状恢复技术。
