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https://issues.apache.org/jira/browse/LUCENE-4922?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13630054#comment-13630054
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David Smiley commented on LUCENE-4922:
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Thanks for your interest Hatim!
Your assessment of just needing to extend SpatialPrefixTree is mostly correct.
It also involves implementing Cell (formerly known as Node) which is tightly
related. There are lots of potential optimizations here. As part of this
task, modifying SpatialPrefixTree & Cell itself is absolutely okay if we find
better (more optimized) ways of doing things, though we need to retain
backwards compatibility with the two existing SpatialPrefixTree implementations
-- geohash & quad. *If* retaining that backwards compatibility turns out to be
too constraining on making this SPT be even better, then we could make SPT an
interface. But the general API of SPT & Cell should be the same as it is now.
What will help in this task is to know that there are extensive tests of the
PrefixTree based spatial search strategies, such that if supplying a new SPT
causes a failure, then you know you've got a bug ;-). But there are few unit
level tests of the SPT itself, and so knowing precisely what is broken could be
hard.
You are correct that the bonus wishes are purely optional optimizations, time
permitting. Very optional; in general I want to see that without these
optimizations that the SPT is as good as it can reasonably be. It _may_ turn
out that these geo specific optimizations have extra runtime costs (such as
calculating the sin() a lot or complexity that make it not worthwhile; I don't
know.
> A SpatialPrefixTree based on the Hilbert Curve and variable grid sizes
> ----------------------------------------------------------------------
>
> Key: LUCENE-4922
> URL: https://issues.apache.org/jira/browse/LUCENE-4922
> Project: Lucene - Core
> Issue Type: New Feature
> Components: modules/spatial
> Reporter: David Smiley
> Assignee: David Smiley
> Labels: gsoc2013, mentor, newdev
>
> My wish-list for an ideal SpatialPrefixTree has these properties:
> * Hilbert Curve ordering
> * Variable grid size per level (ex: 256 at the top, 64 at the bottom, 16 for
> all in-between)
> * Compact binary encoding (so-called "Morton number")
> * Works for geodetic (i.e. lat & lon) and non-geodetic
> Some bonus wishes for use in geospatial:
> * Use an equal-area projection such that each cell has an equal area to all
> others at the same level.
> * When advancing a grid level, if a cell's width is less than half its
> height. then divide it as 4 vertically stacked instead of 2 by 2. The point
> is to avoid super-skinny cells which occurs towards the poles and degrades
> performance.
> All of this requires some basic performance benchmarks to measure the effects
> of these characteristics.
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