# What is the difference between the pose of a robot and the configuration of a robot?

Do "configuration" and "pose" means the same thing? If not what is the difference?

Do "configuration" and "pose" means the same thing?

No.

One of the most clear definitions of 'pose' that I've heard is in Peter Corke's Robotics, Vision and Control (RVC). It states that:

"The position and orientation of a coordinate frame is known as its pose and is shown graphically as a set of coordinate axes. The relative pose of a frame with respect to a reference coordinate frame is denoted by the symbol ξ".

The following figure is figure 2.2 in RVC:

The point P can be described by coordinate vectors relative to either frame {A} or {B}. The pose of {B} relative to {A} is $$^{A} ξ _{B}$$

The 'configuration' of a robot is a set of scalar parameters that specify the positions of all of the robot's points relative to some fixed coordinate system. This can be expressed as a vector of positions and orientations, for example:

q = ($$x$$, $$y$$, $$\theta$$)

or

q = (($$x$$, $$y$$, $$z$$, $$\alpha$$, $$\beta$$, $$\gamma$$))

The set of all possible configurations is the 'configuration space', or 'C-space'.

If we consider the two-link planar manipulator with 2 revolute joints (2R-arm), shown here (taken from fig 7.3 in RVC):

The configuration can be expressed in terms of just the two joint angles $$\theta _{1}$$ and $$\theta _{2}$$, while the configuration space is the set of all possible combinations of the joint angles $$\theta _{1}$$ and $$\theta _{2}$$.

Note that configurations are not necessarily unique. For this robot, there are two possible configurations that result in the same end-effector position, but the end effector will have a different orientation in each case.

A worked example using MATLAB can be found in the Analyzing a 2-joint planar robot arm lesson on Peter's QUT Robot academy. This includes a visual description of the 2R-arm shown above.