Drake: We have both drake::SpatialForce and drake::multibody::SpatialForce defined

[sherm1]

drake::SpatialForce is defined in common/eigen_types.h basically as a typedef for a Vector6, and is only lightly used within RigidBodyPlant and Valkyrie. OTOH, drake::multibody::SpatialForce is a force-space SpatialVector providing essential functionality in the new MultibodyTree code.

The names conflict in typical programs that include namespace drake and drake::multibody (discovered by @mitiguy while making multibody tests). We should get rid of the typedef asap. Since the code it is in will soon be deprecated, it would be fine to give it a somewhat awkward name like RBSpatialForce. Many other solutions are possible.

[amcastro-tri]

Thank you for filing this issue, I had forgotten about this typedef.

[amcastro-tri]

This is the typedef in eigen_types.h:
template <typename Scalar> using SpatialForce = Eigen::Matrix<Scalar, 6, 1>;

Within the same file we have a more appropriate typedef for this, Vector6<T>, in consistency with all other typedefs in the same file. If you all agree I will go ahead and replace drake::SpatialForce<T> with drake::Vector6<T> to avoid any possible collisions for now until this code is deprecated. RBP and Valkyrie code could actually be easily update to use drake::multibody::SpatialForce<T>.

[sherm1]

Per f2f we need to look more closely at @mitiguy's test to see why he's seeing a conflict but @amcastro-tri doesn't.

[sherm1]

Recently rediscovered. Relevant Slack discussion.

[amcastro-tri]

12 uses of SpatialForce<double> in the attic. We could replace with Vector6<double> and remove drake::SpatialForce from eigen_types.h?