opencv+flann库+GenericIndex类

template<typename Distance >

cv::flann::GenericIndex< Distance >::GenericIndex	(	const Mat &	features,
		const ::cvflann::IndexParams &	params,
		Distance	distance = Distance()
	)

类的作用：根据给定数据集构建最近邻搜索索引

参数：

features 包含特征（点）的矩阵，用于索引。矩阵的大小等于num_feature（特征数）× feature_dimensionality（特征维数）（原文：The size of the matrix is num_features x feature_dimensionality） 矩阵元素的数据类型必须和索引类型相同。

params  包含索引参数的结构体（原文：Structure containing the index parameters）索引的类型将取决于该参数的类型。

distance 该方法使用具有指定参数的指定算法从一组特征构造快速搜索结构，如params所定义。

 params是对以下类IndexParams后代之一的引用：

• LinearIndexParams When passing an object of this type, the index will perform a linear, brute-force search. :
  struct LinearIndexParams : public IndexParams

  {

  };
• KDTreeIndexParams When passing an object of this type the index constructed will consist of a set of randomized kd-trees which will be searched in parallel. :
  struct KDTreeIndexParams : public IndexParams

  {

  KDTreeIndexParams( int trees = 4 );

  };
• KMeansIndexParams When passing an object of this type the index constructed will be a hierarchical k-means tree. :
  struct KMeansIndexParams : public IndexParams

  {

  KMeansIndexParams(

  int branching = 32,

  int iterations = 11,

  flann_centers_init_t centers_init = CENTERS_RANDOM,

  float cb_index = 0.2 );

  };
• CompositeIndexParams When using a parameters object of this type the index created combines the randomized kd-trees and the hierarchical k-means tree. :
  struct CompositeIndexParams : public IndexParams

  {

  CompositeIndexParams(

  int trees = 4,

  int branching = 32,

  int iterations = 11,

  flann_centers_init_t centers_init = CENTERS_RANDOM,

  float cb_index = 0.2 );

  };
• LshIndexParams When using a parameters object of this type the index created uses multi-probe LSH (by Multi-Probe LSH: Efficient Indexing for High-Dimensional Similarity Search by Qin Lv, William Josephson, Zhe Wang, Moses Charikar, Kai Li., Proceedings of the 33rd International Conference on Very Large Data Bases (VLDB). Vienna, Austria. September 2007) :
  struct LshIndexParams : public IndexParams

  {

  LshIndexParams(

  unsigned int table_number,

  unsigned int key_size,

  unsigned int multi_probe_level );

  };
• AutotunedIndexParams When passing an object of this type the index created is automatically tuned to offer the best performance, by choosing the optimal index type (randomized kd-trees, hierarchical kmeans, linear) and parameters for the dataset provided. :
  struct AutotunedIndexParams : public IndexParams

  {

  AutotunedIndexParams(

  float target_precision = 0.9,

  float build_weight = 0.01,

  float memory_weight = 0,

  float sample_fraction = 0.1 );

  };
• SavedIndexParams This object type is used for loading a previously saved index from the disk. :
  struct SavedIndexParams : public IndexParams

  {

  SavedIndexParams( String filename );

  };

参数介绍可以看这篇文章：https://blog.youkuaiyun.com/app_12062011/article/details/51987352