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https://issues.apache.org/jira/browse/LUCENE-6191?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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David Smiley resolved LUCENE-6191.
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Resolution: Fixed
One little change in the committed version is a convenience method on
PrefixTreeStrategy, which also gives the capability a bit more visibility.
> 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
>
> Attachments: LUCENE-6191__Spatial_heatmap.patch,
> LUCENE-6191__Spatial_heatmap.patch, LUCENE-6191__Spatial_heatmap.patch
>
>
> 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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