SIFT特征点匹配与消除错配：BBF，RANSAC [2]

 kd_root = kdtree_build( feat2, n2 );。

/** a node in a k-d tree */

struct kd_node{

     int ki;                      /**< partition key index */

     double kv;                   /**< partition key value */

     int leaf;                    /**< 1 if node is a leaf, 0 otherwise */

     struct feature* features;    /**< features at this node */

     int n;                       /**< number of features */

     struct kd_node* kd_left;     /**< left child */

     struct kd_node* kd_right;    /**< right child */

};