XYZ - which direction is positive Z

Question

XYZ - which direction is positive Z

I'm new to the 3D world. I've been learning Motion, along with New Tek's Lightwave. I'm confused about the Z axis. I know that with X, negative is on the left and positive is on the right. With Y, positive is on top, negative is on the bottom. In the APTS Motion book, page 97, positive Z is toward me, and negative Z is away from me. In Lightwave, a 3D animation program, it's the opposite; that is, negative Z is toward me and positive Z is away from me. Certainly, I would imagine, Lightwave would have it right because the fundamental core of the program is centered around the XYZ coordinate system. So, which is right?

Motion 5, Mac OS X (10.7.5), XYZ

Posted on Jul 15, 2013 7:01 PM

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Answer 1

GFXZen

Level 4

1,997 points

Jul 15, 2013 9:55 PM in response to zannamochaccina

The short answer is both are correct...for the particular application. If you look into different applications that use Cartesian coordinate system(Maya, Lightwave, Max, Cinema, Blender, Motion etc.) you mayfind find variations in the +/- direction when talking about near and far. You may even ecounter Z-up instead of Y-up or variations in rotation order (xyz, zyx, yzx). It's not a matter of one applications interpretation of +/- direction is "right" or "wrong", it's just the way each was designed. Personally, I'd strong recomend you not start to think of it as black or white issue. What's most important is to understand the general concept of the Cartesian coordinate system and then stay flexable as you switch between applications or learn new applications.

Note: Rotations order is important because of something called "Gimble Lock". Do a google search for better explanation than I can provide.

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Answer 2

Jul 16, 2013 10:33 AM in response to zannamochaccina

Thank you, GFXZen! You answer was very helpful. My brother was right--again!

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