Answer L8-C1

** Here are the correct answers to this question:

* Answer D "Yaw, pitch and roll sensor in the correction step" is correct.
* Answer A is NOT correct.
* Answer B is NOT correct.
* Answer C is NOT correct.
* Answer E is NOT correct.
* Answer F is NOT correct.

** Explanation

The question is about the robot localisation and the sensors used for it in a case of solar panel cleaning. On the right there is an illustration of a solar panel on an inclined roof. The question is: "You have to design a small (1dm3) mobile robot used for cleaning of solar panels (see picture). You have planned a wheel encoder on your robot, but you have to improve the position estimation made by a Kalman filter. You can choose only one additional sensor, which one do you choose? In which step of the filtering do you use it? Prediction or Correction?". 

Here the prediction and correction are the two main steps of the Kalman filter. The first give a prediction based on the control action, the second makes a correction based on external information captured by sensors.

Six statements are proposed:

* Statement A. "Yaw, pitch and roll sensor in the prediction step" is wrong. This sensor does not give a proprioceptive information, which would be needed in the prediction step, but an information based on the environment (gravity). Only proprioceptive sensors can be used in the prediction step. 
In the explanation of the student we would like to see that they understand that the "Yaw, pitch and roll sensor" is not a proprioceptive sensor.

Statement B. "Gyroscope in the prediction step" is interesting but bringing less than using the Yaw, pitch and roll sensor in the sensing step, giving absolute orientation.
In the explanation of the student we would like to see that they understand that solution D is better, even if this one is interesting.


Statement C. "Wheel speed in the prediction step" is interesting but bringing less than using the Yaw, pitch and roll sensor in the sensing step, giving absolute orientation. Moreover there is already an encoder and the wheel speed will bring less.
In the explanation of the student we would like to see that they understand that solution D is better, and here the fact that there is already an encoder reduces even more the interest of this solution.

Statement D. "Yaw, pitch and roll sensor in the correction step" is the correct solution, helping with a critical element which is the orientation, and this by using an absolute sensor, which is very interesting, as it has no drift.
In the explanation of the student we would like to see that they understand that this sensor brings an absolute information on orientation, which is super valuable. 

Statement E. "Gyroscope in the correction step" makes no sense, the gyro cannot detect environmental elements. 
In the explanation of the student we would like to see that they understand that this is a proprioceptive sensor and cannot be used in the correction step, as it measures nothing in the environment. 

Statement F. "Wheel speed in the correction step" makes no sense, this sensor cannot detect environmental elements.
In the explanation of the student we would like to see that they understand that this is a proprioceptive sensor and cannot be used in the correction step, as it measures nothing in the environment. 