Question

2. What is your subject? COMPUTER GRAPHICS

Question 5: Elaborate the world space or world coordinate systems.

Answer 1

When doing computer graphics, it's useful to have a "universal" coordinate system independent of the camera, so that no matter where your camera is, the objects' coordinates don't change.

That's "world coordinates". The world coordinate system is whatever you define it to be. Which direction is +x, +y, and +z is up to you. Whether 1.0 corresponds to 1.0 metre or 1.0 nanometre is also up to you. Everything will work as long as you are consistent.

However, just having the world coordinates system is not enough in practice.

For example, when you define models that can be placed anywhere in the world, you don't want to define the vertices in world coordinates. Instead, you define a point in the model to be the origin, assume an orientation and scale, and specify the vertices in that coordinate system instead. That's "model coordinates". The coordinates are only transformed to world coordinates when the model is actually placed in the world. This allows you to use the same object in many places, instead of having to make a new one every time (and things would get really complicated in that case if objects can move).

So world and model coordinates give you convenient ways to define where everything is relative to each other, and also define objects that can be placed anywhere in the world.

Then you have camera coordinates. When you actually need to render the world as seen from a camera at a particular point in the world, you need to know where everything is relative to the camera. That's camera coordinates.

However, that's not all you need to render something. The camera coordinates (where objects are relative to the camera) are still in 3D, and we have 2D screens (even when you are rendering 3D, by the way), so there needs to be a final transformation that goes from camera coordinates to screen coordinates. Screen coordinates would be like pixels on your screen.