K Nearest Neighbors 这里的教程看起来很全面

http://people.revoledu.com/kardi/tutorial/KNN/index.html

这里有个三维knn的源码

GLTree:Fast K-Nearest Neighbors Search
http://www.advancedmcode.org/gltree.html
FAST K-NEAREST NEIGHBOURS SEARCH 3D VERSION
http://www.mathworks.com/matlabcentral/fileexchange/24607
这里是前一个版本,貌似解说更详细
http://www.advancedmcode.org/gltree-pro-version-a-fast-nearest-neighbour-library-for-matlab-and-c.html
http://www.advancedmcode.org/gltree-matlab-example-knnsearch-function.html
这里的matlab的代码下载资源很丰富

Efficient K-Nearest Neighbor Search using JIT
http://www.mathworks.com/matlabcentral/fileexchange/19345