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https://issues.apache.org/jira/browse/LUCENE-7069?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15241291#comment-15241291
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David Smiley commented on LUCENE-7069:
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If the Bits (doc set) filter is sparsely populated, then I agree -- you're
better off just doing a typical sort. If I recall (it's been years now), my
implementation did that. But if it's heavily populated, then I picked a fairly
large grid cell (possibly including some adjacent cells if the query point was
close to an edge) and did a distance sort with that rectangle a filter. If I
not only met the topN budget but the furthest distance in that topN was close
enough such that, if I inscribed a circle from the query point to that last
point, that the circle would be completely within the cells making the filter,
then I'm done. If unlucky, I had to iterate up to larger cells/filters or give
up and fall back to a standard distance sort. I recall this made a world of
difference to an app that previously always distance sorted. To be clear, to
the extent that this used the grid cells, it was only as an approximate filter.
the points were always in DocValues and the distance was computed from that.
> Add LatLonPoint.nearest to find closest indexed point to a given query point
> ----------------------------------------------------------------------------
>
> Key: LUCENE-7069
> URL: https://issues.apache.org/jira/browse/LUCENE-7069
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Michael McCandless
> Assignee: Michael McCandless
> Fix For: master, 6.1
>
> Attachments: LUCENE-7069.patch, LUCENE-7069.patch, LUCENE-7069.patch,
> LUCENE-7069.patch
>
>
> KD trees (used by Lucene's new dimensional points) excel at finding "nearest
> neighbors" to a given query point ... I think we should add this to Lucene's
> sandbox as:
> {noformat}
> public static Document nearest(IndexReader r, String field, double lat,
> double lon) throws IOException
> {noformat}
> I only implemented the 1 nearest neighbor for starters ... I think we can
> easily generalize this in the future to K nearest.
> It could also be generalized to more than 2 dimensions, but for now I'm
> making the class package private in sandbox for just the geo2d (lat/lon) use
> case.
> I don't think this should go into 6.0.0, but should go into 6.1: it's a new
> feature, and we need to wrap up and ship 6.0.0 already ;)
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