C語言實現一個四叉樹(quadtree)

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用C語言實現一個2維四叉樹quadtree,具有一定的實際意義。你可以把幾何圖形的索引(用long型的id標識)放到這個樹中(根據最小邊界矩形)。quadtree可以用來快速地區尋找圖形,雖然不是那麼精確,但是畢竟沒有漏掉的。雖然quadtree的效率不如RTree?但是RTree的實現畢竟複雜了些,我會儘快收集整理出RTree的代碼。RTree確實比QuadTree好的多?(起碼RTree很時髦啊!)

標頭檔如下:

/*
 * quadtree.h
 *        Quad tree structure -- for spatial quick searching
 *        cheungmine
 *      Oct. 5, 2007.  All rights reserved.
 */
#ifndef QUADTREE_H_INCLUDED
#define QUADTREE_H_INCLUDED

#include "unistd.h"

#include "list.h"

#define QUAD_SUBNODES 4

#define QBOX_OVERLAP_MAX 0.4
#define QBOX_OVERLAP_MIN 0.02

#define QTREE_DEPTH_MAX 8
#define QTREE_DEPTH_MIN 4

#define QUADRANT_BITS  3

/* a quadrant defined below:

        NW(1)   |    NE(0)
        -----------|-----------
        SW(2)   |    SE(3)
*/
typedef enum
{
    NE = 0,
    NW = 1,
    SW = 2,
    SE = 3
}QuadrantEnum;

/* a box defined below:
           _____max
          |__|__|
          |__|__|
   min
*/
typedef struct _quadbox_t
{   
    double _xmin,
        _ymin,
        _xmax,
        _ymax;
}quadbox_t;

/* quad node */
typedef struct _quadnode_t
{
    quadbox_t  _box;  /* node bound box */
    list_t   *_lst;  /* node data list */
    struct _quadnode_t  *_sub[QUAD_SUBNODES];  /* pointer to subnodes of this node */
}quadnode_t;

/* quad tree */
typedef struct _quadtree_t
{
    quadnode_t *_root;
    int    _depth;  /* max depth of tree: 0-based */
    float   _overlap;  /* overlapped ratio of quanbox */
}quadtree_t;


/*=============================================================================
                        Public Functions
=============================================================================*/
/* creates a quadtree and returns a pointer to it */
extern  quadtree_t*
quadtree_create (quadbox_t    box,
                 int  depth,  /* 4~8 */
                 float overlap /* 0.02 ~ 0.4 */
                 );

/* destroys a quad tree and free all memory */
extern  void
quadtree_destroy (IN  quadtree_t  *qtree
                  );

/* inserts a node identified by node_key into a quadtree, returns the node quadtree encoding */
extern  quadnode_t *
quadtree_insert (IN  quadtree_t            *qtree,
                 IN  long                 node_key,
                 IN  quadbox_t            *node_box
                 );

/* searches nodes inside search_box */
extern  void
quadtree_search (IN  const quadtree_t    *qtree,
                  IN  quadbox_t            *search_box,
                 OUT list_t                *results_list
                 );

#endif // QUADTREE_H_INCLUDED

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