Thank you but I already did it. I check the existence of the field and his type ( an ip address ) before to apply geoip.
In fact when i set logstash output on stdout{} i get all the information that i want ( like the geoip field ), but when i set logstash output on elacticsearch and use a tempate to define the field as a geo_point, elasticsearch save it as a number and not a geo_point so i can't use the map visualization in kibana. This is my current issue.