Add a scoring DistanceQuery that does not need caches and separate filters
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Key: LUCENE-2395
URL: https://issues.apache.org/jira/browse/LUCENE-2395
Project: Lucene - Java
Issue Type: Improvement
Components: contrib/spatial
Reporter: Uwe Schindler
Fix For: 3.1
In a chat with Chris Male and my own ideas when implemnting for PANGAEA, I
thought about the broken distance query in contrib. It lacks the folloing
features:
- It needs a query for the encldoing bbox (which is constant score)
- It needs a separate filter for filtering out distances
- 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 borken for multi-segment search)
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 distance.
This query is almost finished in my head, it just needs coding :-)
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