In that situation, callbacks are currently not supported. What is your use case exactly, or why do you need to use Ik or path planning from that location?
There are workarounds for this, but not that straightforward...
I'm using IK to generate linear paths for the robot arm during some manipulation tasks. The callback function is used to check for collisions during planning. I checked the IK and OMPL documents and I didn't find an easier way for collision checking. Is there any demo or example to show how to add collision checking without using validation callback?
Right now, if you want to use a state validation callback or simIK.findConfig (also with a validation callback), you'll have to set-up a Python ZeroMQ remote API client in a separate thread.
Otherwise you can use simOMPL.setCollisionPairs, which will internally simply check the two+ entities for collision.
But we can implement the callback functionality for situations like yours... need to evaluate a few options...