Spherical
=========

A spherical joint creates a frame that is rotated relative to an existing frame using a quaternion to define its orientation. Initial quaternion values are defined using an equivalent Euler angle sequence. 
**Keyword Arguments**

:param str name: Name given to the joint, default is uppercase characters in alphabetical order (A, B, C, ...)

:param str ref_point_key: Start point from which the vector component of the joint is defined

:param str ref_frame_key: Reference frame in which the translational and rotational displacement components are defined

:param str rotation_sequence: 'ZYX', 'XYZ', 'ZXZ', 'ZYZ', 'XYX', or 'XZX', represents the Euler angle sequence used for defining equivalent initial quaternion states

**Initial Values**

:param numeric initial_r0: Initial value for the 0^{th} rotation angle in the Euler sequence

:param numeric initial_r1: Initial value for the 1^{st} rotation angle in the Euler sequence

:param numeric initial_r2: Initial value for the 2^{nd} rotation angle in the Euler sequence

:param numeric rate_r0: Initial value for angular rotation rate about the x-axis of the created frame

:param numeric rate_r1: Initial value for angular rotation rate about the y-axis of the created frame

:param numeric rate_r2: Initial value for angular rotation rate about the z-axis of the created frame