looking for service to query map occupancy [closed]

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Greetings fellow developers,

I am currently using ROS Fuerte in Ubuntu 12.04. I used the map_server package to read a map. Now I need a service that returns an occupancy value for a given position. Currently, there is only one service in map_server which returns the whole map and I have to probably convert the one dimensional pixel data in to two dimensional positions.
I was told that already a service that does this exists, is anyone aware of such service?

Thank you in advance!