Thank you Anhlqn for the advise. I tried to convert the coordinates to geo_point and get the following error in logstash:
Error: Cannot register filter mutate plugin. The error reported is: Invalid conversion type 'geo_point', expected one of 'string,integer,float,boolean' You may be interested in the '--configtest' flag which you can use to validate logstash's configuration before you choose to restart a running system.
It seems the geo_point option is not available, unless I am missing something?