Question

我正在尝试在python中创建一个Quadtree结构来检测多边形之间的碰撞，而且我已经走得很远（见帖子的结尾）。但是，我意识到这个结构只适用于 points ，因为我决定将对象放在哪个叶子的中心位置。

所以我需要弄清楚如何修改这个四叉树以便我能够检测到区域的碰撞（就像一个圆圈！）。

我可以通过几种不同的方式来考虑这样做：

只将对象放在它们完全填充的节点中 - 这似乎效率低下，因为四叉树的整个要点是将对象放在叶子中以便于搜索/检索并减少我检索的对象数量。
将对象放入与其重叠的每个叶子中 - 这似乎是一个很好的解决方案，但我不完全确定如何处理重叠决策（我想知道这是否效率低下）。< / LI>
??? - 有更好的解决方案吗？

选项＃2（将对象放在多个节点中），我觉得最好在对象周围绘制一个边界矩形，然后使用对象的范围来决定将它放入哪个叶子 - - 但这需要有效地插入每个对象4次（每个角落一个），这似乎是解决问题的低效方法。

有什么更好的建议吗？

    class Quadtree(object):
    """
    A simple Quadtree implementation.  This works with any child object that has a getPosition() method that returns a list or tuple.
    """
    def __init__(self, depth, min_x, min_y, max_x, max_y):
        self.mDepth = depth
        self.mMaxDepth = 4
        self.mMinX = min_x
        self.mMaxX = max_x
        self.mMidX = (max_x - min_x) / 2.0
        self.mMinY = min_y
        self.mMaxY = max_y
        self.mMidY = (max_y - min_y) / 2.0
        self.mHasChildren = False
        self.mMaxChildren = 8
        self.mChildren = []
        self.mSubtrees = []

    def insert(self, newChild):
       """
       Insert an object into the tree.  Returns True if the insert was successful, False otherwise.
       """
       if self.mSubtrees:
           #if subtrees exist, add the child to the subtrees
           index = getIndex(newChild)
           if index != -1:
               self.mSubtrees[index].insert(newChild)
               return True

       #if no subtrees exist, add the child to the child list.
       self.mChildren.append(newChild)

       #and then check if we need to split the tree
       #if there are more than the max children, and we haven't maxed out the tree depth, and there are no subtrees yet
       if len(self.mChildren) > self.mMaxChildren and self.mDepth < self.mMaxDepth and not self.mSubtrees:
           split()
           for child in self.mChildren:
               index = getIndex(child)
               if index != -1:
                   self.mSubtrees[index].insert(child)
           return True

       return False

    def retrieveNeighbors(self, targetChild):
       index = getIndex(targetChild)
       if index != -1 and self.mSubtrees:
           return self.mSubtrees[index].retrieve(targetChild)
       return self.mChildren

    def getIndex(self, child):
       """
       Returns the index of the node that the object belongs to.  Returns -1 if the object does not exist in the tree.
       """
       index = -1
       childPosition = child.getPosition()
       #check if it fits in the top or bottom
       isInTopQuadrant = childPosition[1] > self.mMidY and childPositoin[1] < self.mMaxY
       #check if it fits left
       if childPosition[0] < self.mMidX and childPosition[0] > self.mMinX:
           if isInTopQuadrant:
               index = 1
           else:
               index = 2
       #check if it fits right
      if childPosition[0] > self.mMidX and childPosition[0] < self.mMidX:
          if isInTopQuadrant:
              index = 0
          else:
              index = 3

      return index

    def split(self):
       """
       Split the trees into four subtrees.
       """
       #top right
       self.mSubtrees.append(Quadtree(depth + 1, self.mMidX, self.mMidY, self.mMaxX, self.mMaxY))
       #top left
       self.mSubtrees.append(Quadtree(depth + 1, self.mMinX, self.mMidY, self.mMidX, self.mMaxY))
       #bottom left
       self.mSubtrees.append(Quadtree(depth + 1, self.mMinX, self.mMinY, self.mMidX, self.mMidY))
       #bottom right
       self.mSubtrees.append(Quadtree(depth + 1, self.mMidX, self.mMinY, self.mMaxX, self.mMidY))

    def clear(self):
       """
       Clears the quadtree of children, and all subtrees of children.
       """
       self.mChildren[:] = []
       self.mHasChildren = False
       for tree in range(0,4):
           if self.mSubtrees[tree].mHasChildren:
               self.mSubtrees[tree].clear()

Answer 1

我到目前为止找到的最好的方法是修改_get_index()以检查粒子的整个大小 - 如果它不完全适合子树，那么它就变成了一个孩子父节点：

def _get_index(self, child):
    """
    Returns the index of the node that the object belongs to.  Returns -1 if the object does not exist in the tree.
    """
    index = -1
    child_position = child.get_position()
    child_radius = child.get_radius()
    if len(child_position) != 2:
        print "Quadtree is only designed to handle two-dimensional objects! Object will not be added."
        return index
    #check if it fits in the top or bottom
    is_in_top_quadrant = child_position[1] - child_radius > self.mid_y and child_position[1] + child_radius < self.max_y
    #check if it fits left
    if child_position[0] + child_radius < self.mid_x and child_position[0] - child_radius > self.min_x:
        if is_in_top_quadrant:
            index = 1
        else:
            index = 2
    #check if it fits right
    if child_position[0] - child_radius > self.mid_x and child_position[0] + child_radius < self.mid_x:
        if is_in_top_quadrant:
            index = 0
        else:
            index = 3
    return index

然后retrieve_neighbors()可以遍历树并添加它传递的每个节点的子节点，一直到叶节点。

如何有效地将非点对象插入到四叉树中

1 个答案: