danrosher opened a new pull request, #940:
URL: https://github.com/apache/solr/pull/940

   https://issues.apache.org/jira/browse/SOLR-16292
   
   # Description
   
   
[N-Vector](https://en.wikipedia.org/wiki/N-vector#Example:_Great_circle_distance)
 is a three-parameter representation that can be used to calculate the 
great-circle distance (assuming a spherical Earth).
   
   For small distances it compares well with Math.acos, and is a faster way of 
calculating the great-circle distance than Haversine.
   
   # Solution
   
   Store N-Vectors in solr index via CoordinateFieldType with 3 values for the 
nvector into single value double subfields, use java Math class for indexing 
these
   Use an maclaurin approximation for acos for calculating great-circle 
distance at query-time via a function query
   
   # Tests
   
   Tests for the FastInvTrigTest impl to compare it's acos with Math.acos.
   Tests for NVectorUtil, NVectorDist , latLongToNVector and NVectorToLatLong
   Tests for indexing N-Vectors and calculating the great-circle distance via 
the function query.
   
   # Checklist
   
   Please review the following and check all that apply:
   
   - [x] I have reviewed the guidelines for [How to 
Contribute](https://wiki.apache.org/solr/HowToContribute) and my code conforms 
to the standards described there to the best of my ability.
   - [x] I have created a Jira issue and added the issue ID to my pull request 
title.
   - [x] I have given Solr maintainers 
[access](https://help.github.com/en/articles/allowing-changes-to-a-pull-request-branch-created-from-a-fork)
 to contribute to my PR branch. (optional but recommended)
   - [x] I have developed this patch against the `main` branch.
   - [ ] I have run `./gradlew check`.
   - [x] I have added tests for my changes.
   - [ ] I have added documentation for the [Reference 
Guide](https://github.com/apache/solr/tree/main/solr/solr-ref-guide)
   


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