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From "Uwe Schindler (JIRA)" <>
Subject [jira] Updated: (LUCENE-2395) Add a scoring DistanceQuery that does not need caches and separate filters
Date Thu, 15 Apr 2010 16:00:57 GMT


Uwe Schindler updated LUCENE-2395:


A first idea of the Query, it does not even compile as some classes are missing (coming with
Chris' later patches), but it shows how it should work and how its customizeable.

> Add a scoring DistanceQuery that does not need caches and separate filters
> --------------------------------------------------------------------------
>                 Key: LUCENE-2395
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: contrib/spatial
>            Reporter: Uwe Schindler
>             Fix For: 3.1
>         Attachments:
> In a chat with Chris Male and my own ideas when implementing for PANGAEA, I thought about
the broken distance query in contrib. It lacks the following features:
> - It needs a query/filter for the enclosing bbox (which is constant score)
> - It needs a separate filter for filtering out hits to far away (inside bbox but outside
distance limit)
> - It has no scoring, so if somebody wants to sort by distance, he needs to use the custom
sort. For that to work, spatial caches distance calculation (which is broken for multi-segment
> The idea is now to combine all three things into one query, but customizeable:
> We first thought about extending CustomScoreQuery and calculate the distance from FieldCache
in the customScore method and return a score of 1 for distance=0, score=0 on the max distance
and score<0 for farer hits, that are in the bounding box but not in the distance circle.
To filter out such negative scores, we would need to override the scorer in CustomScoreQuery
which is priate.
> My proposal is now to use a very stripped down CustomScoreQuery (but not extend it) that
does call a method getDistance(docId) in its scorer's advance and nextDoc that calculates
the distance for the current doc. It stores this distance also in the scorer. If the distance
> maxDistance it throws away the hit and calls nextDoc() again. The score() method will
reurn per default weight.value*(maxDistance - distance)/maxDistance and uses the precalculated
distance. So the distance is only calculated one time in nextDoc()/advance().
> To be able to plug in custom scoring, the following methods in the query can be overridden:
> - float getDistanceScore(double distance) - returns per default: (maxDistance - distance)/maxDistance;
allows score customization
> - DocIdSet getBoundingBoxDocIdSet(Reader, LatLng sw, LatLng ne) - returns an DocIdSet
for the bounding box. Per default it returns e.g. the docIdSet of a NRF or a cartesian tier
filter. You can even plug in any other DocIdSet, e.g. wrap a Query with QueryWrapperFilter
> - support a setter for the GeoDistanceCalculator that is used by the scorer to get the
> - a LatLng provider (similar to CustomScoreProvider/ValueSource) that returns for a given
doc id the lat/lng. This method is called per IndexReader one time in scorer creation and
will retrieve the coordinates. By that we support FieldCache or whatever.
> This query is almost finished in my head, it just needs coding :-)

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