Research NN searching method FLANN 近邻近似搜索算法已经集成到OpenCV中，在OpenCV中有一个模块就是flann，其中基本就是在FLANN库的基础上进行简单更改集成的。有的时候我们任务中如果想单独使用该模块，可以直接对其编译成动态链接库，编写接口进行调用。本项目就是对FLANN进行编译，然后直接进行相应调用使用的测试。
- download source code
- make sure install the following packages: cmake libhdf5-dev libgtest-dev :这个库最好是自己下载只有进行自己编译，这个编译过程比较好 mpi 和mp等库
- update CMakeList.txt for example: I haven't install matlab in my machine and I set the Matlab bind from ON to OFF.
- cmake ..
sudo make all NOTE: make process may have a long time in virtul machine, and the process may be halt in somewhere, please wait... sudo make install - 检查是否有相应的python接口，如果有的话就太棒了。所幸的是flann已经有实现python的接口，不过我们可以学习一下python如何调用c,c++的动态连接库的。 * 包括数据类型的对应关系的设定,和动态库的加载
python from ctypes import (Structure, c_char_p, c_int, c_float, c_uint, c_long, c_void_p, cdll, POINTER) def load_flann_library(): root_dir = os.path.abspath(os.path.dirname(__file__)) libnames = ['libflann.so'] libdir = 'lib' if sys.platform == 'win32': libnames = ['flann.dll', 'libflann.dll'] elif sys.platform == 'darwin': libnames = ['libflann.dylib'] while root_dir is not None: for libname in libnames: try: #print 'Trying ',os.path.join(root_dir,'lib',libname) flannlib = cdll[os.path.join(root_dir, libdir, libname)] return flannlib except Exception: pass try: flannlib = cdll[os.path.join(root_dir, 'build', libdir, libname)] return flannlib except Exception: pass tmp = os.path.dirname(root_dir) if tmp == root_dir: root_dir = None else: root_dir = tmp # if we didn't find the library so far, try loading without # a full path as a last resort for libname in libnames: try: #print 'Trying',libname flannlib = cdll[libname] return flannlib except: pass return None
* 定义接口的返回类型和参数的对应关系
Flann 参考手册 Muja, M., & Lowe, D. G. (2014). Scalable nearest neighbor algorithms for high dimensional data. IEEE Transactions on Pattern Analysis & Machine Intelligence, 36(11), 2227-2240. FLANN库全称是Fast Library for Approximate Nearest Neighbors，它是目前最完整的（近似）最近邻开源库。不但实现了一系列查找算法，还包含了一种自动选取最快算法的机制。