improve performance of FastPolygonOperations constructor #33
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replaces old O(n²) polygon slicing implementation with a quad-recursive O(n log(n)) algorithm.
tyrasd
commented
Oct 10, 2018
| Geometry[] result = new Geometry[numBands*numBands]; | ||
| traverseQuads(bandIterations, 0,0, env, geom, gf, result); | ||
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| blocks = new ArrayList<>(Arrays.asList(result)); |
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actually, one could store the result directly as a Geometry[] variable in this.blocks (instead of the current ArrayList<Geometry> wrapper). But in order to stay binary compatible with current 0.5 code (that could be already running on an Ignite cluster for example 😉 ), it's probably better to keep it as it for now and change it in a later major version (0.6).
tyrasd
added
the
performance
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Some quick & dirty benchmarks (timings are for a full oshdb-api request including oshdb processing time, ignite data serialization and other ohsome-api overhead):
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rtroilo
approved these changes
Oct 22, 2018
rtroilo
approved these changes
Oct 22, 2018
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Replaces the straight-forward
O(n²)polygon slicing implementation with a quad-recursiveO(n log(n))algorithm (assuming that JTS' intersection method takes O(n) time to compute the intersection of a n-vertex polygon with another 4 vertex polygon). A minor additional change is that now, the number of bands is rounded up to the next power of two (mainly to make the implementation easier).