opencv/3rdparty/flann/kdtree_index.h

/***********************************************************************
 * Software License Agreement (BSD License)
 *
 * Copyright 2008-2009  Marius Muja (mariusm@cs.ubc.ca). All rights reserved.
 * Copyright 2008-2009  David G. Lowe (lowe@cs.ubc.ca). All rights reserved.
 *
 * THE BSD LICENSE
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 * modification, are permitted provided that the following conditions
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 * 1. Redistributions of source code must retain the above copyright
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 *    notice, this list of conditions and the following disclaimer in the
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 *************************************************************************/

#ifndef KDTREE_H
#define KDTREE_H

#include <algorithm>
#include <map>
#include <cassert>

#include "heap.h"
#include "common.h"
#include "constants.h"
#include "allocator.h"
#include "matrix.h"
#include "result_set.h"
#include "random.h"
#include "nn_index.h"
#include "saving.h"

using namespace std;


namespace cvflann
{


/**
 * Randomized kd-tree index
 *
 * Contains the k-d trees and other information for indexing a set of points
 * for nearest-neighbor matching.
 */
class KDTreeIndex : public NNIndex
{

	enum {
		/**
		 * To improve efficiency, only SAMPLE_MEAN random values are used to
		 * compute the mean and variance at each level when building a tree.
		 * A value of 100 seems to perform as well as using all values.
		 */
		SAMPLE_MEAN = 100,
		/**
		 * Top random dimensions to consider
		 *
		 * When creating random trees, the dimension on which to subdivide is
		 * selected at random from among the top RAND_DIM dimensions with the
		 * highest variance.  A value of 5 works well.
		 */
		RAND_DIM=5
	};


	/**
	 * Number of randomized trees that are used
	 */
	int numTrees;

	/**
	 *  Array of indices to vectors in the dataset.  When doing lookup,
	 *  this is used instead to mark checkID.
	 */
	int* vind;

	/**
	 * An unique ID for each lookup.
	 */
	int checkID;

	/**
	 * The dataset used by this index
	 */
	const Matrix<float> dataset;

    int size_;
    int veclen_;


    float* mean;
    float* var;


	/*--------------------- Internal Data Structures --------------------------*/

	/**
	 * A node of the binary k-d tree.
	 *
	 *  This is   All nodes that have vec[divfeat] < divval are placed in the
	 *   child1 subtree, else child2., A leaf node is indicated if both children are NULL.
	 */
	struct TreeSt {
		/**
		 * Index of the vector feature used for subdivision.
		 * If this is a leaf node (both children are NULL) then
		 * this holds vector index for this leaf.
		 */
		int divfeat;
		/**
		 * The value used for subdivision.
		 */
		float divval;
		/**
		 * The child nodes.
		 */
		TreeSt *child1, *child2;
	};
	typedef TreeSt* Tree;

    /**
     * Array of k-d trees used to find neighbors.
     */
    Tree* trees;
    typedef BranchStruct<Tree> BranchSt;
    typedef BranchSt* Branch;
    /**
     * Priority queue storing intermediate branches in the best-bin-first search
     */
    Heap<BranchSt>* heap;


	/**
	 * Pooled memory allocator.
	 *
	 * Using a pooled memory allocator is more efficient
	 * than allocating memory directly when there is a large
	 * number small of memory allocations.
	 */
	PooledAllocator pool;



public:

    flann_algorithm_t getType() const
    {
        return KDTREE;
    }

	/**
	 * KDTree constructor
	 *
	 * Params:
	 * 		inputData = dataset with the input features
	 * 		params = parameters passed to the kdtree algorithm
	 */
	KDTreeIndex(const Matrix<float>& inputData, const KDTreeIndexParams& params = KDTreeIndexParams() ) : dataset(inputData)
	{
        size_ = dataset.rows;
        veclen_ = dataset.cols;

        numTrees = params.trees;
        trees = new Tree[numTrees];

		// get the parameters
//        if (params.find("trees") != params.end()) {
//        	numTrees = (int)params["trees"];
//        	trees = new Tree[numTrees];
//        }
//        else {
//        	numTrees = -1;
//        	trees = NULL;
//        }
		heap = new Heap<BranchSt>(size_);
		checkID = -1000;

		// Create a permutable array of indices to the input vectors.
		vind = new int[size_];
		for (int i = 0; i < size_; i++) {
			vind[i] = i;
		}

        mean = new float[veclen_];
        var = new float[veclen_];
	}

	/**
	 * Standard destructor
	 */
	~KDTreeIndex()
	{
		delete[] vind;
		if (trees!=NULL) {
			delete[] trees;
		}
		delete heap;
        delete[] mean;
        delete[] var;
	}


	/**
	 * Builds the index
	 */
	void buildIndex()
	{
		/* Construct the randomized trees. */
		for (int i = 0; i < numTrees; i++) {
			/* Randomize the order of vectors to allow for unbiased sampling. */
			for (int j = size_; j > 0; --j) {
// 				int rand = cast(int) (drand48() * size);
				int rnd = rand_int(j);
				assert(rnd >=0 && rnd < size_);
				swap(vind[j-1], vind[rnd]);
			}
			trees[i] = NULL;
			divideTree(&trees[i], 0, size_ - 1);
		}
	}



    void saveIndex(FILE* stream)
    {
    	save_header(stream, *this);
    	save_value(stream, numTrees);
    	for (int i=0;i<numTrees;++i) {
    		save_tree(stream, trees[i]);
    	}
    }



    void loadIndex(FILE* stream)
    {
    	IndexHeader header = load_header(stream);

    	if (header.rows!=size() || header.cols!=veclen()) {
    		throw FLANNException("The index saved belongs to a different dataset");
    	}
    	load_value(stream, numTrees);

    	if (trees!=NULL) {
    		delete[] trees;
    	}
    	trees = new Tree[numTrees];
    	for (int i=0;i<numTrees;++i) {
    		load_tree(stream,trees[i]);
    	}
    }



    /**
    *  Returns size of index.
    */
    int size() const
    {
        return size_;
    }

    /**
    * Returns the length of an index feature.
    */
    int veclen() const
    {
        return veclen_;
    }


	/**
	 * Computes the inde memory usage
	 * Returns: memory used by the index
	 */
	int usedMemory() const
	{
		return  pool.usedMemory+pool.wastedMemory+dataset.rows*sizeof(int);   // pool memory and vind array memory
	}


    /**
     * Find set of nearest neighbors to vec. Their indices are stored inside
     * the result object.
     *
     * Params:
     *     result = the result object in which the indices of the nearest-neighbors are stored
     *     vec = the vector for which to search the nearest neighbors
     *     maxCheck = the maximum number of restarts (in a best-bin-first manner)
     */
    void findNeighbors(ResultSet& result, const float* vec, const SearchParams& searchParams)
    {
        int maxChecks = searchParams.checks;

        if (maxChecks<0) {
            getExactNeighbors(result, vec);
        } else {
            getNeighbors(result, vec, maxChecks);
        }
    }


	void continueSearch(ResultSet& result, float* vec, int maxCheck)
	{
		BranchSt branch;

		int checkCount = 0;

		/* Keep searching other branches from heap until finished. */
		while ( heap->popMin(branch) && (checkCount < maxCheck || !result.full() )) {
			searchLevel(result, vec, branch.node,branch.mindistsq, checkCount, maxCheck);
		}

		assert(result.full());
	}


//    Params estimateSearchParams(float precision, Dataset<float>* testset = NULL)
//    {
//        Params params;
//
//        return params;
//    }


private:


    void save_tree(FILE* stream, Tree tree)
    {
    	save_value(stream, *tree);
    	if (tree->child1!=NULL) {
    		save_tree(stream, tree->child1);
    	}
    	if (tree->child2!=NULL) {
    		save_tree(stream, tree->child2);
    	}
    }


    void load_tree(FILE* stream, Tree& tree)
    {
    	tree = pool.allocate<TreeSt>();
    	load_value(stream, *tree);
    	if (tree->child1!=NULL) {
    		load_tree(stream, tree->child1);
    	}
    	if (tree->child2!=NULL) {
    		load_tree(stream, tree->child2);
    	}
    }


	/**
	 * Create a tree node that subdivides the list of vecs from vind[first]
	 * to vind[last].  The routine is called recursively on each sublist.
	 * Place a pointer to this new tree node in the location pTree.
	 *
	 * Params: pTree = the new node to create
	 * 			first = index of the first vector
	 * 			last = index of the last vector
	 */
	void divideTree(Tree* pTree, int first, int last)
	{
		Tree node;

		node = pool.allocate<TreeSt>(); // allocate memory
		*pTree = node;

		/* If only one exemplar remains, then make this a leaf node. */
		if (first == last) {
			node->child1 = node->child2 = NULL;    /* Mark as leaf node. */
			node->divfeat = vind[first];    /* Store index of this vec. */
		} else {
			chooseDivision(node, first, last);
			subdivide(node, first, last);
		}
	}




	/**
	 * Choose which feature to use in order to subdivide this set of vectors.
	 * Make a random choice among those with the highest variance, and use
	 * its variance as the threshold value.
	 */
	void chooseDivision(Tree node, int first, int last)
	{
        memset(mean,0,veclen_*sizeof(float));
        memset(var,0,veclen_*sizeof(float));

		/* Compute mean values.  Only the first SAMPLE_MEAN values need to be
			sampled to get a good estimate.
		*/
		int end = min(first + SAMPLE_MEAN, last);
		int count = end - first + 1;
		for (int j = first; j <= end; ++j) {
			float* v = dataset[vind[j]];
            for (int k=0; k<veclen_; ++k) {
                mean[k] += v[k];
            }
		}
        for (int k=0; k<veclen_; ++k) {
            mean[k] /= count;
        }

		/* Compute variances (no need to divide by count). */
		for (int j = first; j <= end; ++j) {
			float* v = dataset[vind[j]];
            for (int k=0; k<veclen_; ++k) {
                float dist = v[k] - mean[k];
                var[k] += dist * dist;
            }
		}
		/* Select one of the highest variance indices at random. */
		node->divfeat = selectDivision(var);
		node->divval = mean[node->divfeat];

	}


	/**
	 * Select the top RAND_DIM largest values from v and return the index of
	 * one of these selected at random.
	 */
	int selectDivision(float* v)
	{
		int num = 0;
		int topind[RAND_DIM];

		/* Create a list of the indices of the top RAND_DIM values. */
		for (int i = 0; i < veclen_; ++i) {
			if (num < RAND_DIM  ||  v[i] > v[topind[num-1]]) {
				/* Put this element at end of topind. */
				if (num < RAND_DIM) {
					topind[num++] = i;            /* Add to list. */
				}
				else {
					topind[num-1] = i;         /* Replace last element. */
				}
				/* Bubble end value down to right location by repeated swapping. */
				int j = num - 1;
				while (j > 0  &&  v[topind[j]] > v[topind[j-1]]) {
					swap(topind[j], topind[j-1]);
					--j;
				}
			}
		}
		/* Select a random integer in range [0,num-1], and return that index. */
// 		int rand = cast(int) (drand48() * num);
		int rnd = rand_int(num);
		assert(rnd >=0 && rnd < num);
		return topind[rnd];
	}


	/**
	 *  Subdivide the list of exemplars using the feature and division
	 *  value given in this node.  Call divideTree recursively on each list.
	*/
	void subdivide(Tree node, int first, int last)
	{
		/* Move vector indices for left subtree to front of list. */
		int i = first;
		int j = last;
		while (i <= j) {
			int ind = vind[i];
			float val = dataset[ind][node->divfeat];
			if (val < node->divval) {
				++i;
			} else {
				/* Move to end of list by swapping vind i and j. */
				swap(vind[i], vind[j]);
				--j;
			}
		}
		/* If either list is empty, it means we have hit the unlikely case
			in which all remaining features are identical. Split in the middle
            to maintain a balanced tree.
		*/
		if ( (i == first) || (i == last+1)) {
            i = (first+last+1)/2;
		}

		divideTree(& node->child1, first, i - 1);
		divideTree(& node->child2, i, last);
	}



	/**
	 * Performs an exact nearest neighbor search. The exact search performs a full
	 * traversal of the tree.
	 */
	void getExactNeighbors(ResultSet& result, const float* vec)
	{
		checkID -= 1;  /* Set a different unique ID for each search. */

		if (numTrees > 1) {
            fprintf(stderr,"It doesn't make any sense to use more than one tree for exact search");
		}
		if (numTrees>0) {
			searchLevelExact(result, vec, trees[0], 0.0);
		}
		assert(result.full());
	}

	/**
	 * Performs the approximate nearest-neighbor search. The search is approximate
	 * because the tree traversal is abandoned after a given number of descends in
	 * the tree.
	 */
	void getNeighbors(ResultSet& result, const float* vec, int maxCheck)
	{
		int i;
		BranchSt branch;

		int checkCount = 0;
		heap->clear();
		checkID -= 1;  /* Set a different unique ID for each search. */

		/* Search once through each tree down to root. */
		for (i = 0; i < numTrees; ++i) {
			searchLevel(result, vec, trees[i], 0.0, checkCount, maxCheck);
		}

		/* Keep searching other branches from heap until finished. */
		while ( heap->popMin(branch) && (checkCount < maxCheck || !result.full() )) {
			searchLevel(result, vec, branch.node,branch.mindistsq, checkCount, maxCheck);
		}

		assert(result.full());
	}


	/**
	 *  Search starting from a given node of the tree.  Based on any mismatches at
	 *  higher levels, all exemplars below this level must have a distance of
	 *  at least "mindistsq".
	*/
	void searchLevel(ResultSet& result, const float* vec, Tree node, float mindistsq, int& checkCount, int maxCheck)
	{
		if (result.worstDist()<mindistsq) {
//			printf("Ignoring branch, too far\n");
			return;
		}

		float val, diff;
		Tree bestChild, otherChild;

		/* If this is a leaf node, then do check and return. */
		if (node->child1 == NULL  &&  node->child2 == NULL) {

			/* Do not check same node more than once when searching multiple trees.
				Once a vector is checked, we set its location in vind to the
				current checkID.
			*/
			if (vind[node->divfeat] == checkID || checkCount>=maxCheck) {
				if (result.full()) return;
			}
            checkCount++;
			vind[node->divfeat] = checkID;

			result.addPoint(dataset[node->divfeat],node->divfeat);
			return;
		}

		/* Which child branch should be taken first? */
		val = vec[node->divfeat];
		diff = val - node->divval;
		bestChild = (diff < 0) ? node->child1 : node->child2;
		otherChild = (diff < 0) ? node->child2 : node->child1;

		/* Create a branch record for the branch not taken.  Add distance
			of this feature boundary (we don't attempt to correct for any
			use of this feature in a parent node, which is unlikely to
			happen and would have only a small effect).  Don't bother
			adding more branches to heap after halfway point, as cost of
			adding exceeds their value.
		*/

		float new_distsq = flann_dist(&val, &val+1, &node->divval, mindistsq);
//		if (2 * checkCount < maxCheck  ||  !result.full()) {
		if (new_distsq < result.worstDist() ||  !result.full()) {
			heap->insert( BranchSt::make_branch(otherChild, new_distsq) );
		}

		/* Call recursively to search next level down. */
		searchLevel(result, vec, bestChild, mindistsq, checkCount, maxCheck);
	}

	/**
	 * Performs an exact search in the tree starting from a node.
	 */
	void searchLevelExact(ResultSet& result, const float* vec, Tree node, float mindistsq)
	{
		if (mindistsq>result.worstDist()) {
			return;
		}

		float val, diff;
		Tree bestChild, otherChild;

		/* If this is a leaf node, then do check and return. */
		if (node->child1 == NULL  &&  node->child2 == NULL) {

			/* Do not check same node more than once when searching multiple trees.
				Once a vector is checked, we set its location in vind to the
				current checkID.
			*/
			if (vind[node->divfeat] == checkID)
				return;
			vind[node->divfeat] = checkID;

			result.addPoint(dataset[node->divfeat],node->divfeat);
			return;
		}

		/* Which child branch should be taken first? */
		val = vec[node->divfeat];
		diff = val - node->divval;
		bestChild = (diff < 0) ? node->child1 : node->child2;
		otherChild = (diff < 0) ? node->child2 : node->child1;


		/* Call recursively to search next level down. */
		searchLevelExact(result, vec, bestChild, mindistsq);
		float new_distsq = flann_dist(&val, &val+1, &node->divval, mindistsq);
		searchLevelExact(result, vec, otherChild, new_distsq);
	}

};   // class KDTree

}

#endif //KDTREE_H