docs: private KNNHeap linearScan(Relation<? extends O> relation, DBIDIter iter, final O obj, KNNHeap heap) {
      final PrimitiveDistanceFunction<? super O> rawdist = this.rawdist;
      double max = Double.POSITIVE_INFINITY;
      while(iter.valid()) {
        final double dist = rawdist.distance(obj, relation.get(iter));
        if(dist <= max) {
          max = heap.insert(dist, iter);
        }
        iter.advance();
      }
      return heap;
    }