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https://issues.apache.org/jira/browse/LUCENE-4186?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13421495#comment-13421495
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David Smiley commented on LUCENE-4186:
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I'd like to look at the bigger picture with distance error. I think there are
two things a user might want to specify:
# What is the maximum distance detail the index should use for its calculations
on this field. In geospatial contexts, this might be 1 meter. As applied to
geohash prefix tree based Strategies this would result in using a particular
maxLevels (geohash length) for the tree of about 10.
# What is the maximum error distance for a particular shape that I am indexing
or querying by? It is bounded by the previous statistic. I might want to
specify this in real distance terms (e.g. 1 meter) or have it be some fraction
or percentage tied to the shape's size, which makes a nice default.
These end up being hints / constraints; a Strategy will very likely use more
precision but should have at least as much precision as is asked for. Sound
good? If so...
So would SpatialStrategy then have a setMaxDetailDist() and
setDefaultDistErrPct() (for index & query shapes) ? The problem with
setMaxDetailDist is that, as a setter, it's done after the Strategy's
construction; we don't have an init() method. It could become another
constructor argument, the 3rd: SpatialStrategy(SpatialContext ctx, String
fieldName, maxDetailDist) or maybe don't worry about it -- add a
getMaxDetailDist() that returns the actual maximum detail distance, and let
initialization be up to the specific Strategy. I guess I like that best.
setDefaultDistErrPct() could be a simple setter with getter. Supplying 0
implies maximum detail allowed by maxDetailDist.
> Lucene spatial's "distErrPct" is treated as a fraction, not a percent.
> ----------------------------------------------------------------------
>
> Key: LUCENE-4186
> URL: https://issues.apache.org/jira/browse/LUCENE-4186
> Project: Lucene - Core
> Issue Type: Bug
> Components: modules/spatial
> Reporter: David Smiley
> Assignee: David Smiley
> Priority: Critical
> Fix For: 4.0
>
>
> The distance-error-percent of a query shape in Lucene spatial is, in a
> nutshell, the percent of the shape's area that is an error epsilon when
> considering search detail at its edges. The default is 2.5%, for reference.
> However, as configured, it is read in as a fraction:
> {code:xml}
> <fieldType name="location_2d_trie"
> class="solr.SpatialRecursivePrefixTreeFieldType"
> distErrPct="0.025" maxDetailDist="0.001" />
> {code}
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