public override DocIdSet GetDocIdSet(Lucene.Net.Index.IndexReader reader)
{
var geoHashValues = FieldCache_Fields.DEFAULT.GetStrings(reader, _geoHashField);
int docBase = NextDocBase;
NextDocBase += reader.MaxDoc();
return new GeoHashFilteredDocIdSet(StartingFilter.GetDocIdSet(reader), geoHashValues, DistanceLookupCache, _lat, _lng, docBase, Distance, Distances);
}