How to get the distance between two objects (meshes)

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Hello all

I am interesting in wright a plugin that calculates the distance between my robot and the objects around it. My intention is to use this measure in order to grade the performance of obstacle avoidance algorithms. Therefore, i am looking for some kind of unambiguous world state data, and not a sensor simulation.

My question: is there a function in the Gazebo API that performs these kind of calculations, that i can use it in my plugin ?

thanks.