3D Modelling and Animation

1 State what is meant by a vertex, an edge and a face in a 3D model. 3

One mark for each of the following, to a maximum of 3.

• A vertex is a point in 3D space
• An edge is a line connecting two vertices
• A face is a flat surface enclosed by edges

Model answer. A vertex is a single point in three dimensional space, defined by its x, y and z coordinates. An edge is a straight line connecting two vertices. A face is a flat surface enclosed by edges, usually a triangle or a four sided shape, and together the vertices, edges and faces form the mesh that makes up the object.

2 Explain why a model used in a video game usually has fewer polygons than the same character in an animated film. 4

One mark for each of the following, to a maximum of 4.

• A game must render frames in real time as the player plays
• Around 60 frames must be produced every second
• A film renders each frame once in advance, taking as long as needed
• Fewer polygons means the game runs smoothly, with textures used to suggest detail

Model answer. A video game has to produce each frame in real time while the player is controlling the character, which means the computer typically has less than a sixtieth of a second to work out lighting, positions and surfaces for the entire scene. If a model contains too many polygons the machine cannot keep up and the frame rate drops, which makes the game feel unresponsive and unplayable. An animated film has no such constraint, because each frame is rendered once in advance and can take minutes or even hours on a render farm, so millions of polygons per character are affordable. Game artists therefore use much simpler meshes and rely on detailed textures and lighting tricks to suggest detail that is not actually modelled, which costs almost no performance while looking convincing on screen.

3 Describe how keyframes are used to create an animation. 3

One mark for each of the following, to a maximum of 3.

• The animator sets values at particular frames
• These are the keyframes marking the start and end of a movement
• The software calculates the frames in between by interpolation

Model answer. Rather than creating every single frame by hand, the animator sets the position, rotation or other property of an object at a small number of important moments, and each of these is recorded as a keyframe. For example, a keyframe at frame 1 might place a ball on the left of the screen and a keyframe at frame 48 might place it on the right. The software then calculates all the frames in between automatically, a process called interpolation, gradually changing the value from one keyframe to the next. The animator can adjust how that change happens, for example using easing so the movement accelerates and slows rather than travelling at a constant speed, which looks far more natural.

4 An animation lasts 90 seconds and runs at 25 frames per second. Each frame takes 4 minutes to render. Calculate the total render time in hours. 4

One mark for each of the following, to a maximum of 4.

• Calculates the number of frames as 25 x 90
• Obtains 2250 frames
• Multiplies by 4 minutes to get 9000 minutes
• Converts to 150 hours

Model answer. The total number of frames is the frame rate multiplied by the duration, so 25 x 90 = 2250 frames. Each frame takes 4 minutes, so the total render time is 2250 x 4 = 9000 minutes. Dividing by 60 converts this to 150 hours, which is over six days of continuous rendering on a single machine, and this is exactly why studios use render farms of hundreds of computers working on different frames at the same time.

5 Explain the purpose of a texture in 3D modelling. 3

One mark for each of the following, to a maximum of 3.

• A texture is an image applied to the surface of a model
• It adds visual detail without adding polygons
• This keeps the model efficient while still looking detailed

Model answer. A texture is a two dimensional image that is wrapped onto the surface of a 3D model, using UV mapping to ensure it lines up correctly on a curved or complex shape. Its purpose is to add visual detail such as wood grain, brickwork, rust or fabric weave without adding any extra geometry to the model. This matters enormously for performance: modelling every individual brick in a wall would require an enormous number of polygons and slow the scene down, whereas a single flat face with a brick texture looks convincing and costs almost nothing to render.