There is a well-known schism in the world of computer graphics. People who create computer graphics for games tend to think differently from people who create computer graphics for movies and animation.
In a three dimensional X,Y,Z coordinate system, people who work in game development usually think of the Z coordinate as pointing up toward the sky. In contrast, people who create computer graphics for movies and animation often think of the Y coordinate as pointing up toward the sky.
I think this is due to the fundamental problem each is trying to solve. A person who is designing a computer game starts out by thinking about strategy: How does a character move about in the world? Does the character need to go over a bridge? Storm a castle? Escape from a room?
These are the sorts of questions you tend to ask while looking at a map. So the first two coordinates a game designer thinks about — the X and the Y — are the ones that describe the geography of the game world. The Z coordinate is then added later for height above the terrain, to create a 3D game experience.
In contrast, a filmmaker asks questions in terms of the final image: How will this composition look in my movie? Is this a head shot or an establishing shot? Are these two characters looking at each other?
These are the sorts of questions you tend to ask while looking at a movie screen. So the first two coordinates a film designer thinks about — the X and the Y — are the ones that describe the image on that screen. The Z coordinate is then added later for depth into and out of the screen, to add visual layers to the image.
Practically speaking, this has sometimes led to some difficulty in the business. Some software is designed with the “Z is up” convention and other software is designed with the “Y is up” convention.
Everything works great until you try to use these various software programs together. Then again, whoever said art was supposed to be easy?