Question

请注意我对解决问题的最有效方法感兴趣，而不是寻求使用特定库的建议。

我有大量（~200,000）的2D形状（矩形，多边形，圆形等），我想将它们分类成重叠的组。例如，在图片中，绿色和橙色将标记为组1，黑色，红色和蓝色将标记为组2.

我们会说我会获得list<Shape>。缓慢的解决方案是：

（我没有运行此代码 - 只是一个示例算法）

// Everything initialized with groupid = 0
int groupid = 1;

for (int i = 0; i < shapes.size(); ++i)
{
    if (shapes[i].groupid)
    {
        // The shape hasn't been assigned a group yet
        // so assign it now
        shapes[i].groupid = groupid;
        ++groupid;
    }

    // As we compare shapes, we may find that a shape overlaps with something
    // that was already assigned a group. This keeps track of groups that
    // should be merged.
    set<int> mergingGroups = set<int>();

    // Compare to all other shapes
    for (int j = i + 1; j < shapes.size(); ++j)
    {
        // If this is one of the groups that we are merging, then
        // we don't need to check overlap, just merge them
        if (shapes[j].groupid && mergingGroups.contains(shapes[j].groupid))
        {
            shapes[j].groupid = shapes[i].groupid;
        }
        // Otherwise, if they overlap, then mark them as the same group
        else if (shapes[i].overlaps(shapes[j]))
        {
            if (shapes[j].groupid >= 0)
            {
                // Already have a group assigned
                mergingGroups.insert(shapes[j].groupid;
            }
            // Mark them as part of the same group
            shapes[j].groupid = shapes[i].groupid
        }
    }
}

更快的解决方案是将对象放入空间树中以减少j对象重叠比较（内循环）的数量，但我仍然需要迭代其余的以合并组。 / p>

有什么更快的吗？

谢谢！

Answer 1

希望这有助于某人 - 这就是我实际实现的（伪代码）。

tree = new spatial tree
for each shape in shapes
    set shape not in group 
    add shape to tree 

for each shape in shapes
    if shape in any group 
        skip shape

    cur_group = new group
    set shape in cur_group 

    regions = new stack
    insert bounds(shape) into regions

    while regions has items
        cur_bounds = pop(regions)

        for test_shape in find(tree, cur_bounds)
            if test_shape has group
                skip test_shape

            if overlaps(any in cur_group, test_shape)
                insert bounds(tester) into regions
                set test_shape group = cur_group

Answer 2

如果您有效地找到了空间树的所有成对交叉点，则可以使用union-find algorithm对对象进行分组

如何将形状分组为多组重叠形状

2 个答案: