[MUSIC] Before we talk about the objects that make up our virtual world, we have to think about the space in which these objects exist. And this comes down to really understanding how we represent things like objects and positions in a computer. Everything on a computer really has to be represented as numbers. Even something like an image, or a video, is broken down into vast quantities of little numbers, several for each pixels. To understand how we do that, I'd like to start not with 3D yet, but with 2D images that make up the screen of a computer. If you think about a computer screen, it's made up of a whole bunch of pixels. Massive grids of pixels, rows and rows and rows of pixels but they essentially make up a grid like the one I'm showing you now. So how do we represent the position of a pixel as a number? First we start at the top-left and call that pixel 0. In fact, we call it 0,0, because as we will see in a minute, we need two numbers. If we count how many pixels across a particular pixel is, in this case it's 12 pixels. And we also need to know how many pixels down it is. It's 8 pixels. These two numbers tell us exactly where a pixel is on a computer screen. Just like the latitude and longitude on a map tell us where we are in the world. We call the number of pixels across x and the number of pixels down, y. That's just an ancient mathematical tradition. So with the numbers x and y, we can represent the positions of any pixel on the screen. And that allows us to draw things at particular positions on the screen. For example, if we want a pixel at the top right, we need a high number for x and a low number for y. At the bottom left, on the other hand we want a low X, and a high Y. For the bottom right, both should be high. We don't really need to think anymore in terms of pixels. We can just think of x and y as distances. They can be meters or inches. All we need is two numbers and that gives us the position of any point in 2D space. That's really powerful. With two points, we can draw a line between them. And with three lines, we can make a triangle. We can start to make shapes so that this is the basic building block of objects in 2D space. In 3D, we can still think of it in exactly the same way. The only difference is, as well as being able to go up and down and across, we can also go in and out. We need a third number, and we call this number unsurprisingly Z. Thee numbers x, y and z are what represent any position in 3D space. And you will see over and over again, that we're using x and y and z as our basic coordinates. So they're giving us add points. And once we have that, we can start using x's, y's and zs to create full 3D objects. [MUSIC]