On Wed, Dec 1, 2010 at 7:27 AM, Nic Roets <[email protected]> wrote: > Hello Scott, > > How do you keep track of what bboxs each entity belongs to ?
An Int2ShortMultiMap implemented by composing two underlying Int2ShortMap implementations with different space efficiency tradeoffs, a custom sparsearray implementation based on http://google-sparsehash.googlecode.com/svn/trunk/doc/implementation.html, and one imported from a library of java collections specialized to primitive types ('fastutils') that uses a standard hashtable. The hybrid has a memory overhead of about 4 bytes per node output, storing 750m keys with 800m vals in 3.2gb of heap. The approach for generating an Int2ShortMultiMap from several Int2ShortMap's is by layering them. When put()ing keys, I store in Int2ShortMap[0], but if the key is already there, I try Int2ShortMap[1], ..... until I find one that is free. I create additional maps as needed. For dense maps, sparsehash is the more efficient implementation, and for non-dense maps at the higher layers, a hashtable is the more efficient implementation. To avoid checking each bbox for each point, used a simpler design than a quadtree or r-tree as andrzej suggests, some precomputing and binary searches at a cost of (sqrt(n)) instead of O(log n) for mostly non-overlapping-regions. > > I'm not really asking a question, I'm just saying that I found a way to > reduce the memory requirement for that considerably. Instead of a bit per > bbox per entry, I store only 16 bits or 32 bits per entry. Here is the > source. > http://trac.openstreetmap.org/browser/applications/rendering/gosmore/bboxSplit.cpp?rev=24484 Definitely. Can you explain how you track the information? You have a much more concise implememtation than mine, but I can't easily figure it out what it is doing from the source code. Scott _______________________________________________ dev mailing list [email protected] http://lists.openstreetmap.org/listinfo/dev
