barrett::units Namespace Reference

Classes
struct	JointTorques
struct	JointPositions
struct	JointVelocities
struct	JointAccelerations
struct	CartesianForce
	Template metafunction yielding the 3-element math::Vector used to represent a Cartesian force. Result available in the nested type typedef. More...
struct	CartesianTorque
	Template metafunction yielding the 3-element math::Vector used to represent a Cartesian torque. Result available in the nested type typedef. More...
struct	CartesianPosition
	Template metafunction yielding the 3-element math::Vector used to represent a Cartesian position. Result available in the nested type typedef. More...
struct	CartesianVelocity
	Template metafunction yielding the 3-element math::Vector used to represent a Cartesian velocity. Result available in the nested type typedef. More...
struct	CartesianAcceleration
	Template metafunction yielding the 3-element math::Vector used to represent a Cartesian acceleration. Result available in the nested type typedef. More...

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Detailed Description

Defines "unit types" that are actually specializations of math::Vector or math::Matrix.

These classes use type information to give meaning to what would otherwise be an anonymous math::Vector of doubles.

For instance, a systems::Wam has two outputs: one for joint positions and one for joint velocities. Though both of these might be (depending on the particular WAM) 7-element arrays of doubles, they represent two different quantities. They are not interchangeable. They have different units. A user might want to design a joint-space position controller and a joint-space velocity controller for the WAM. If the joint position output of the systems::Wam were to be connected to the velocity controller's feedback input, it would almost certainly result in a programmer-caused error. If such a program were run, the robot would not behave as intended and finding the bug could be difficult and time-consuming.

Adding a notion of units to our vectors (units::JointPositions::type, units::JointVelocities::type, etc.) allows us to:

• be explicit about our intents for any given input or parameter
• more closely mimic the mathematical rules that govern our engineering discipline
• help the compiler to help us catch such errors.

This comes without incurring a runtime performance penalty.

Users can easily create their own barrett::units classes by passing any C++ type name (such as the name of a class or struct) as the Units template parameter to math::Vector or math::Matrix. The type void is the default and lifts all compile-time restrictions regarding units.

See also:

math::Vector

math::Matrix

BARRETT_UNITS_TYPEDEFS

BARRETT_UNITS_FIXED_SIZE_TYPEDEFS

BARRETT_UNITS_TEMPLATE_TYPEDEFS