David Smiley created LUCENE-6191:
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Summary: Spatial 2D faceting (heatmaps)
Key: LUCENE-6191
URL: https://issues.apache.org/jira/browse/LUCENE-6191
Project: Lucene - Core
Issue Type: New Feature
Components: modules/spatial
Reporter: David Smiley
Assignee: David Smiley
Fix For: 5.1
Lucene spatial's PrefixTree (grid) based strategies index data in a way highly
amenable to faceting on grids cells to compute a so-called _heatmap_. The
underlying code in this patch uses the PrefixTreeFacetCounter utility class
which was recently refactored out of faceting for NumberRangePrefixTree
LUCENE-5735. At a low level, the terms (== grid cells) are navigated
per-segment, forward only with TermsEnum.seek, so it's pretty quick and
furthermore requires no extra caches & no docvalues. Ideally you should use
QuadPrefixTree (or Flex once it comes out) to maximize the number grid levels
which in turn maximizes the fidelity of choices when you ask for a grid
covering a region. Conveniently, the provided capability returns the data in a
2-D grid of counts, so the caller needn't know a thing about how the data is
encoded in the prefix tree. Well almost... at this point they need to provide
a grid level, but I'll soon provide a means of deriving the grid level based on
a min/max cell count.
I recommend QuadPrefixTree with geo=false so that you can provide a square
world-bounds (360x360 degrees), which means square grid cells which are more
desirable to display than rectangular cells.
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