search

udacity / robotics-nanodegree-issues

Public waffleboard to track Robotics Nanodegree Issues
2 stars 0 forks source link

Lesson 11.7: Composition of rotations multiplies rotations in same direction. #194

Closed ghost closed 6 years ago

ghost commented 6 years ago

In the above mentioned lesson it asks us to code both an intrinsic and an extrinsic rotation, with the difference between these two being the rotation order. However the solutions for both of these code quizzes has the same multiplication order.

ghost commented 6 years ago

This his means that the answers to the two quizzes are different, making the answer to the third quiz, a multiple choice question, incorrect.

jchernus commented 6 years ago

I am seeing the solution to both as being,

YZ_intrinsic_sym = R_y * R_z

Is this the case for you?

ghost commented 6 years ago

Yes, it's the same for me, and as I understand it, the order of multiplication should be different for extrinsic and intrinsic.

sahiljuneja commented 6 years ago

A late response, so I'm hoping you got this clarified somewhere else. But regardless -

The text above the quiz mentions

The first requires you to perform an intrinsic rotation sequence about the Y and then Z axes. The second quiz requires you to perform an extrinsic rotation about the Z and then Y axes.

As per the video, intrinsic rotations are post-multiplied. So , the order of multiplication would be Ry*Rz for the first one (because first rotation is about Y).

Extrinsic rotations are pre-multiplied. So, order of multiplication would be Ry*Rz (because first rotation is about Z).

So, yes. Order in both quizzes are the same. Hope that helped; I'll close the ticket for now.