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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-6699) Integrate lat/lon BKD and spatial3d
Date Wed, 19 Aug 2015 19:56:46 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-6699?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14703646#comment-14703646
] 

Michael McCandless commented on LUCENE-6699:
--------------------------------------------

bq. what's the minimum resolution that BKD expects to descend to?

BKD itself has no resolution limits: it descends to a region that has < N points, at which
point it does a linear scan of those points checking if they match the shape.

But, the encoding we use is limited precision, using 32 bits for each of x, y, z (96 bits
total), with range -1.002 to 1.002.  This means a point that goes in, using 3 doubles, will
be quantized (pixelated).  However, the test takes this into account: when it's computing
the expected value, it does the same pixelation that the doc values encoding did.

So, even miniscule circles should still work correctly?

> Integrate lat/lon BKD and spatial3d
> -----------------------------------
>
>                 Key: LUCENE-6699
>                 URL: https://issues.apache.org/jira/browse/LUCENE-6699
>             Project: Lucene - Core
>          Issue Type: New Feature
>            Reporter: Michael McCandless
>            Assignee: Michael McCandless
>         Attachments: Geo3DPacking.java, LUCENE-6699.patch, LUCENE-6699.patch, LUCENE-6699.patch,
LUCENE-6699.patch, LUCENE-6699.patch, LUCENE-6699.patch, LUCENE-6699.patch, LUCENE-6699.patch,
LUCENE-6699.patch, LUCENE-6699.patch, LUCENE-6699.patch, LUCENE-6699.patch, LUCENE-6699.patch,
LUCENE-6699.patch, LUCENE-6699.patch, LUCENE-6699.patch, LUCENE-6699.patch, LUCENE-6699.patch,
LUCENE-6699.patch, LUCENE-6699.patch, LUCENE-6699.patch
>
>
> I'm opening this for discussion, because I'm not yet sure how to do
> this integration, because of my ignorance about spatial in general and
> spatial3d in particular :)
> Our BKD tree impl is very fast at doing lat/lon shape intersection
> (bbox, polygon, soon distance: LUCENE-6698) against previously indexed
> points.
> I think to integrate with spatial3d, we would first need to record
> lat/lon/z into doc values.  Somewhere I saw discussion about how we
> could stuff all 3 into a single long value with acceptable precision
> loss?  Or, we could use BinaryDocValues?  We need all 3 dims available
> to do the fast per-hit query time filtering.
> But, second: what do we index into the BKD tree?  Can we "just" index
> earth surface lat/lon, and then at query time is spatial3d able to
> give me an enclosing "surface lat/lon" bbox for a 3d shape?  Or
> ... must we index all 3 dimensions into the BKD tree (seems like this
> could be somewhat wasteful)?



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