[SOLVED] C++ spatialindex library: loading/storing main memory RTree from/to disk

C++ spatialindex library: loading/storing main memory RTree from/to disk

I have created a main memory R* index with the help of spatialindex library in the following way (DBStream implements the interface for bulkLoading)

// creating a main memory RTree
memStorage = StorageManager::createNewMemoryStorageManager();

size_t capacity = 1024;
bool bWriteThrough = false;
fileInMem = StorageManager
   ::createNewRandomEvictionsBuffer(*memStorage, capacity, bWriteThrough);

DBStream dstream(streets);

tree = RTree::createAndBulkLoadNewRTree(SpatialIndex::RTree::BLM_STR, dstream,
   *fileInMem,
   fillFactor, indexCapacity,
   leafCapacity, dimension, rv, indexIdentifier);

My data is read-only, i.e., I want to build the tree only once, save it, and reload from persistent storage every time I use my program. Clearly, I can save and load the memStorage myself, but how to recreate the RTree from it?

Solution

Since you are bulk-loading the tree anyway, there is little to gain here, actually. All that a STR bulk load does is sort the data. This is O(n log n) theoretically, but if you have the data sorted appropriately it will actually be in O(n) with most sorting implementations.

So most likely, serializing the tree into a file and back is not much cheaper than bulk-loading it again each time. It does take away some flexibility though.

R-Trees in general are meant for dynamic data IMHO. Sure, they do work for static data. But their key strength (opposed to other structures) is that the tree supports balancing on insert.