final double[] lngIndex = FieldCache.DEFAULT.getDoubles(reader, lngField);
final int docBase = nextDocBase;
nextDocBase += reader.maxDoc();
return new FilteredDocIdSet(startingFilter.getDocIdSet(reader)) {
protected boolean match(int doc) {
double x = latIndex[doc];
double y = lngIndex[doc];
// round off lat / longs if necessary