presto-geospatial/src/main/java/io/prestosql/plugin/geospatial/SpatialPartitioningStateFactory.java/GroupedSpatialPartitioningState/setExtent
class GroupedSpatialPartitioningState:        @Override
        public void setExtent(Rectangle envelope)
        {
            if (envelopes.get(groupId) == null) {
                envelopeCount++;
            }
            envelopes.set(groupId, envelope);
        }