LESSON

Right-Handed 3D Coordinate Frame

Transcript

In the previous lecture when we were discussing 2-dimensional worlds, we introduced the concept of a right-handed coordinate frame. And, just to remind you, the right-handed coordinate frame is constructed like this. We draw the x-axis and then we swing the y-axis up by 90 degrees. A three-dimensional coordinate frame is actually very similar to the two-dimensional coordinate frame. So, here is the two-dimensional right-handed coordinate frame that we just introduced. And, what I’m going to do do now is to rotate that in three dimensions. And, what we see is that the z-axis was previously hidden. Previously, it was sticking up at us out of the screen.

To create a 3-dimensional right-handed coordinate frame, we start in a similar way. We draw the x-axis. We swing the y-axis so that it makes an angle of 90 degrees to the x-axis. And then, we swing the z-axis upwards and it also makes an angle of 90 degrees to the x-axis and also makes an angle of 90 degrees to the y-axis.

There’s a very close relationship between the 2-dimensional and the 3-dimensional coordinate frames. Let me put down the two-dimensional coordinate frame and here is three-dimensional coordinate frame. And, I can overlay the x-axis and the y-axis and we see that the z-axis points upwards. We refer to this as a right-handed coordinate frame. And, the reason we call it a right-handed frame is the orientation of the axes can be defined very simply using my right hand. So, this is the x-axis. This is the y-axis. And, this is the z-axis pointing upwards. So, whenever we’re doing work with 3-dimensional coordinate frames, they are always right-handed coordinate frames.

This particular coordinate frame that I built, we have an x-axis and a y-axis and this one, the z-axis pointing downwards. This is a left-handed coordinate frame. So it’s best not to use these, they are going to cause you all sorts of grief. So, don’t use left-handed coordinate frames. Go with the right-handed coordinate frame.

So, just to recap. When we create a right-handed coordinate frame, we use this rule what’s called the right-handed rule, and I take my right hand. The x-axis is parallel to my thumb. The y-axis is parallel to my index finger. And, the z-axis is parallel to my middle finger.

We discuss the structure of a right-handed 3D coordinate frame and the spatial relationship between its axes which is encoded in the right-hand rule.

Professor Peter Corke

Professor of Robotic Vision at QUT and Director of the Australian Centre for Robotic Vision (ACRV). Peter is also a Fellow of the IEEE, a senior Fellow of the Higher Education Academy, and on the editorial board of several robotics research journals.

Skill level

This content assumes high school level mathematics and requires an understanding of undergraduate-level mathematics; for example, linear algebra - matrices, vectors, complex numbers, vector calculus and MATLAB programming.

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