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From "Ignacio Vera (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-8126) Spatial prefix tree based on S2 geometry
Date Tue, 13 Feb 2018 08:58:00 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-8126?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16362014#comment-16362014
] 

Ignacio Vera commented on LUCENE-8126:
--------------------------------------

[~jpountz], the important thing here is if the shape is close to the equator and close to
the poles. When using bounding boxes, the further away you are from the equator, the more
cells you need to describe a shape. S2 cells are more constant around the globe so it should
use the similar number of cells regardless where you are on the sphere.

I put together an example (attached) where I index a square polygon on the equator and at
a 60 degrees latitude with trees with same set-up. You can see that geohash tree is the more
inneficient as it needs quite a lot of cells to describe the polygon, 260 at the equator and
390 at 60 degrees. S2 and Quad trees use the same number of cells to describe the polygon
at the equator (108) but at 60 degrees, S2 uses a similar number of cells  and Quad tree
almost double the number of cells required. Here is where the benefit comes.

I have attached as well a small graph showing query performance of my data depending on the
SPT. The queries use composite strategy and are random cone searches (query shape is a random
circle). Horizontal axis represents the number of hits of the query and the vertical axis
the query execution time.

 

 

> Spatial prefix tree based on S2 geometry
> ----------------------------------------
>
>                 Key: LUCENE-8126
>                 URL: https://issues.apache.org/jira/browse/LUCENE-8126
>             Project: Lucene - Core
>          Issue Type: New Feature
>          Components: modules/spatial-extras
>            Reporter: Ignacio Vera
>            Assignee: Ignacio Vera
>            Priority: Major
>         Attachments: SPT-query.jpeg, STP-cell.pdf
>
>          Time Spent: 0.5h
>  Remaining Estimate: 0h
>
> Hi [~dsmiley],
> I have been working on a prefix tree based on goggle S2 geometry (https://s2geometry.io/)
to be used mainly with Geo3d shapes with very promising results, in particular for complex
shapes (e.g polygons). Using this pixelization scheme reduces the size of the index, improves
the performance of the queries and reduces the loading time for non-point shapes. 
> If you are ok with this contribution and before providing any code I would like to understand
what is the correct/prefered approach:
> 1) Add new depency to the S2 library (https://mvnrepository.com/artifact/io.sgr/s2-geometry-library-java).
It has Apache 2.0 license so it should be ok.
> 2) Create a utility class with all methods necessary to navigate the S2 tree and create
shapes from S2 cells (basically port what we need from the library into Lucene).
> What do you think?



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