I think is_inverse option is not useful and can be misleading. You have already two functions transform and transform_inverse why do you need the is_inverse option? On the other hand, I think the forward direction is well defined as the moving going to the static. You could call that moving2static as Matthew suggested to make it even more precise if you want. 

I can see that because this is the "symmetric" version you may think of it as making sense to have forward and backwards but as the static and moving are already defined the directions are already defined too so I see no need for inverting their behaviour. You duplicate code for no good reason. But maybe we are wrong. What do you think @omarocegueda ?