Is it possible in Apache Phoenix to create a functional index on an UDF that uses as arguments columns from two different tables?

Question

We need to execute geo-spatial queries where we use geo-spatial functions that operate on columns from two different tables (YELLOW_TAXI_TRIPS, TAXI_ZONES).

The UDF works as a comparison to join the two tables. Below is the query in which we want to improve performance applying a functional index.

SELECT ZONES.zone, count(1) AS hits
FROM YELLOW_TAXI_TRIPS AS TRIPS, TAXI_ZONES AS ZONES
WHERE STWithinFromText('POINT('||TRIPS.PICKUP_LONGITUDE||' '||TRIPS.PICKUP_LATITUDE||')', ZONES.geom)
GROUP BY ZONES.zone;