Getting Frame Transform With Shared Parent

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Because ROS (python indigo at least) does not like reverse traversing the TF tree it won't perform a transform between two frames that share a parent. For example if you have a parent frame Base which has two child frames Left_Wheel and Right_Wheel, ROS will happily find the transform between Base and either child, but cannot find the transform between Left_Wheel and Right_Wheel.

I have a convoluted workaround for this which involves setting up a local transformer, inverting one of the the child transforms and setting it as the parent of the shared parent. This is super unpleasant and has to be done every single time I want to perform this transform. Is there a smarter way to do this?

Thanks