static Ptr cv::ORB::create (

                        int nfeatures = 500,

                         float scaleFactor = 1.2f,

                        int nlevels = 8,

                        int edgeThreshold = 31,

                        int firstLevel = 0,

                         int WTA_K = 2,

                         int scoreType = ORB::HARRIS_SCORE,

                         int patchSize = 31,

                         int fastThreshold = 20

                     ) 

nfeatures:表示取的特征点数量

float scaleFactor = 1.2f   ：表示每一层与上一层的比例关系

int nlevels = 8,：图像金字塔的层数

edgeThreshold = 31,默认吧，看不懂解释

firstLevel = 0,  默认吧，看不懂解释

int WTA_K = 2, 表示描述符随机数的范围，2表示描述符的数字随机取0，1。3表示随机取0，1，2。一般都是2

scoreType = ORB::HARRIS_SCORE,这表示用harris特征来给定分数。一般默认用这个。

patchSize = 31,默认吧，看不懂解释

fastThreshold = 20默认吧，看不懂解释

英文详解：

https://docs.opencv.org/3.2.0/db/d95/classcv_1_1ORB.html#adc371099dc902a9674bd98936e79739c