Recovering Rotation Axis From JointModelRevoluteUnaligned

[Cfather]

Hi, I have a specific coding question.

I have some revolute joints that rotate reversely in the robot. The urdf description for these joints would be something like <axis="0 0 -1">.
My question is: how could I get the information of what the rotation axis is from a pinocchio model.
For example, joints like <axis="0 0 1"> will be parsed as JointModelRZ. And if I print the name of the joint using model.joints[i].shortname(), it will give me a string JointModelRZ and I will be able to know that this is a revolute joint with respect to z axis.
Joints like <axis="0 0 -1"> however, will be parsed as JointModelRevoluteUnaligned so I can't tell from its shortname which axis it rotates.

I noticed that JointModelRevoluteUnalignedTpl contains a vector variable axis that might store this information. However, model.joints[i] stores a JointModelTpl. Is there a way to convert from JointModelTpl to JointModelRevoluteUnalignedTpl so that I can get access to the variable axis and then tell the rotation axis of this joint? I appreciate any ideas!

[jorisv]

Hello @Cfather,

This pull request #2315 have added the getMotionAxis method on joint model with aligned axis.

JointModelTpl inherit from a boost::variant that contains the implemented joint.
You can create boost::static_visitor that will call getMotionAxis for aligned joint and axis for unaligned joint.

[Cfather]

Thanks! Will this appear in future versions of Pinocchio?

[jorisv]

It's already available in Pinocchio 3.2.0.