# Chapter 1a The Building Blocks of 3D

This section covers the basic building blocks and common terminology in the 3D world, although they way they are used changes from program to program, all of these constructs or terms are encountered in just about every 3D application you may pick.  Speaking of which, now might be a good time to select which program you wish to use.  For the modeling examples, I will be using Wings3D.

The Vertex

This is the very most fundamental building block.  A vertex is simply a point in 3 dimensional space.  It is represented by an x,y and z coordinate which represent where that point is located.  All 3D applications allow you to modify at the vertex level but many ( Wings 3D and Blender included ) won’t let you start with a single vertex.

It’s not much to look at, but this is your basic vertex:

In and of itself, nothing special, but as it is pretty much the core of all 3d objects, it’s pretty important. With the exception of particles, you will almost never deal with singular vertices.

The Vector

Generally you don’t really deal with vectors all that often in 3D graphic apps ( but all the time as a programmer ), but they are important enough to be covered.  Basically a vector is a point in 3d space and a direction.  Think of it this way, where ever you currently are, that is a point in 3d space.  Now point at something, you have just created a vector.  A vector goes on forever in the direction pointed.

So, basically, its just a point in space, and a direction.  The individual axis in your 3d application could be considered a vector, that started at the origin ( a point in 3d space at location 0,0,0 ) and continuing forever in their direction.

More commonly though, you deal with Euclidian vectors, which is a vector with a magnitude, or in more plain English, with a length.  So, unlike a pure vector, a Euclidian vector only goes as far as its magnitude.

Here is a Euclidian vector:

In the world of graphics, one very common use of this kind of vector is velocity.  Where the position represents, well, the position, the direction represents the direction of travel and the magnitude represents the speed or velocity.

Again, with the exception of normals, if you are an artist you can probably forget everything I just said!

The Line

We all know more or less what the line is.  Frankly, it’s the connection of two points ( or in a graphical program, vertices ).

There you go, a line.  Nothing fancy really.

The Spline

In mathematical terms, a spline is a piecewise-polynomial real function.  In terms that real humans understand, splines are bendy lines.  In the land of computer graphics, there are tons of different kinds of splines, including b-splines, nurbs-curves, etc.  With the rise of box modeling, the spline has become increasingly less important.  They are still commonly used in pathing.  Anyways, here is a spline of sorts.

The Polygon

A polygon is a shape made up of at least one triangle, most often many more.  Triangles, Quadrangles and n-Gons ( >4 edge ) are all polygons.  However, 3d objects are often made up of many polygons.  A cube, like the picture below, is actually composed of 6 quads.  When modeling, if is often best to work with quads, as they can effortlessly ( by splitting ) can be turned into triangles without altering your shape.  All objects imported into Unity are ultimately composed of triangles only.

Now we actually move into a 3D application for the remainder

The Edge

This is referred to as an edge.  It represented the “edge” of one or more faces.

The Face

This refers to the “solid” bit between the edges.  When dealing with 3D models, this is in general the most visible aspect.  In this case, this is a quad face, as it is composed of 4 edges.  If it was composed of 3 edges, it would be considered a tri-face.

The Vertex

As described earlier, this is the vertex. A location in 3D space that make up the end points of edges.

The Normal

This one is a bit trickier to explain.  See the green lines in the picture to the left?  They represent the faces “normal” or the direction that the face, um… faces.  By default, all faces are one sided and therefore are only visible on the side their normal points. Therefore, the normal represents the direction of a face.

The following illustrates what happens to a polygon if the normals are inverted.  As you can see, everything is basically “inside out”.  This image illustrates the rotation of a cube that has had it’s normals flipped.

Finally, there is the ngon I’ve already mentioned a few times.  For more details on ngons read this post.

Next up, it’s all about the actions you can do with these primitives. Click here to proceed to chapter 1b.

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