Lucene.net proximity search - geolocation

Question

Does anybody have any experience with having lucene.net index latitude and longitude values then return an ordered set of results based on distance from a single point?
Will the Lucene.Net.Spatial library help me at all with this?

Answer 1

A little late to the party but yes, the Spatial library is the place to start with this. The basics behind it are to:
1) Add Lat and Long fields to your document
doc.Add(new Field("Latitude",
NumericUtils.DoubleToPrefixCoded(Latitude),
Field.Store.YES, Field.Index.NOT_ANALYZED));
doc.Add(new Field("Longitude",
NumericUtils.DoubleToPrefixCoded(Longitude),
Field.Store.YES, Field.Index.NOT_ANALYZED));
2) Create plotters for the each tier of granularity that your search needs to support
IProjector projector = new SinusoidalProjector();
var ctp = new CartesianTierPlotter(0, projector,
Fields.LocationTierPrefix);
StartTier = ctp.BestFit(MaxKms);
EndTier = ctp.BestFit(MinKms);
Plotters = new Dictionary<int, CartesianTierPlotter>();
for (var tier = StartTier; tier <= EndTier; tier++)
{
Plotters.Add(tier, new CartesianTierPlotter(tier,
projector,
Fields.LocationTierPrefix));
}
3) Use your plotters to index your document for each tier
private static void AddCartesianTiers(double latitude,
double longitude,
Document document)
{
for (var tier = StartTier; tier <= EndTier; tier++)
{
var ctp = Plotters[tier];
var boxId = ctp.GetTierBoxId(latitude, longitude);
document.Add(new Field(ctp.GetTierFieldName(),
NumericUtils.DoubleToPrefixCoded(boxId),
Field.Store.YES,
Field.Index.NOT_ANALYZED_NO_NORMS));
}
}
With your document indexed you can move onto building a query. This example uses a ConstantScoreQuery but you can swap that out for your ranged scoring:
/* Builder allows us to build a polygon which we will use to limit
* search scope on our cartesian tiers, this is like putting a grid
* over a map */
var builder = new CartesianPolyFilterBuilder(Fields.LocationTierPrefix);
/* Bounding area draws the polygon, this can be thought of as working
* out which squares of the grid over a map to search */
var boundingArea = builder.GetBoundingArea(Latitude,
Longitude,
DistanceInKilometres * ProductSearchEngine.KmsToMiles);
/* We refine, this is the equivalent of drawing a circle on the map,
* within our grid squares, ignoring the parts the squares we are
* searching that aren't within the circle - ignoring extraneous corners
* and such */
var distFilter = new LatLongDistanceFilter(boundingArea,
DistanceInKilometres * KmsToMiles,
Latitude,
Longitude,
ProductSearchEngine.Fields.Latitude,
ProductSearchEngine.Fields.Longitude);
/* We add a query stating we will only search against products that have
* GeoCode information */
var query = new TermQuery(new Term(Fields.HasGeoCode,
FieldFlags.HasField));
/* Add our filter, this will stream through our results and
* determine eligibility */
masterQuery.Add(new ConstantScoreQuery(distanceFilter),
BooleanClause.Occur.MUST);
All of this is taken from a blog post I just wrote whilst looking at a similar problem. You can see it at http://www.leapinggorilla.com/Blog/Read/1005/spatial-search-in-lucenenet