How to attach sensor from gazebo database(.sdf) to urdf model?

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Hi, In gazebo, there are already available models (insert tab) which you can simple insert in your scene. I am having trouble with using it with my urdf model.

I want to add velodyne to my robot. But the problem is that i cannot do this as the model available is in .sdf format. I have tried adding it using this link information http://gazebosim.org/tutorials/?tut=a... but NO LUCK. - -- -- I have also tried this approach but i cannot add velodyne using this approach though i have added different sensors using the same underlying concept: http://gazebosim.org/tutorials?tut=ro...

I am using kinetic.