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最近发现了slam，决定尝试坚持学习，大概率会放弃，但是还是试一试。
读到slam14讲的44页，有些线性代数上的概念忘了，导致看不懂某些部分。
以三维空间为例
正交向量：点积为0的两个向量
单位向量：模为1的向量
单位正交向量：两个单位向量，点积为0
正交基：三个非零向量组成的向量组，就是三维空间的正交基，https://blog.csdn.net/u012421852/article/details/80475497
单位正交基：正交基的每个向量为单位向量。
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