4.1 - 3D Modeling¶
3D modeling is the process of developing a mathematical representation of an object. The result is a 3D model which can be used for rendering 3D scenes or to prototype newly designed widgets. Creating 3D models is an art that requires extensive training. In the movie and game industries people often become experts at 3D modeling and that is their sole job. The next time you watch a movie that contains CGI special effects, notice the number of modelers that are listed in the credits at the end of the film.
Note these characteristics of 3D models:
- The goal is to represent the 3D form of an object, so an object’s surface
is often the only thing that is modeled. There are
exceptions, such as a model for simulating the inner workings of an engine.
- A 3D model is typically a polygonal mesh, which is a set of
connected polygons. Polygons with more than 3 edges are converted to
triangles for rendering. A triangular mesh is a polygonal mesh composed
entirely of triangles.
- The number of polygons used to represent the form of an object determines
the accuracy of the model. More polygons means greater accuracy, but at
the expense of more memory requirements and slower rendering.
- The total number of triangles in a scene is often the deciding factor
in whether the scene can be rendered in less than 1/30th of a second.
It is common to reduce the number of triangles in one model so that
another model can have more.
- A model is manipulated as a unit. If parts of an object move independently, then those parts must be modeled separately. For example, if you have a box with a lid that opens, this would be modeled as two separate objects - a five sided box and a lid.
Modeling Software¶
There are many software applications designed to help a modeler create 3D models. Here is a partial list. Commercial modeling software can be very expensive. For example, a single license for CATIA is $65,000 with an annual maintenance fee of 18% (1). We will use Blender for these tutorials, which is a free, open-source modeling and animation program.
Glossary¶
- 3D model
- a mathematical representation of an object.
- polygon
- a flat area enclosed by a set of connected boundary edges.
- polygonal mesh
- a group of polygons that define the surfaces of an object.
- triangular mesh
- a group of triangles that define the surfaces of an object.
- modeling software
- a software program that facilitates the creation of 3D models.
- modeler
- a person who creates 3D models.
- Blender
- an open-source, free modeling and animation tool.
Self Assessment¶
-
Q-87: Why does a 3D model typically only describe the 3D surfaces of an object?
- For fast rendering, we only describe what is visible to the viewer.
- Correct. If some part of a object will never be rendered, then it is not typically modeled.
- The surface is the object.
- Incorrect. 3D objects are more than just their visible surfaces.
- The surface captures everything there is to know about a 3D object.
- Incorrect. 3D objects are more than just their visible surfaces.
- Most modelers are just lazy.
- Incorrect. Modeling is actually precise, tedious, and hard work.
-
Q-88: To create real-time renderings at 30 frames per second, what is typically one of the
limiting factors on the models in the scene?
- The total number of triangles in the scene.
- Correct. For example, your scene might be limited to 10 models with a 1,000 triangles each.
- The distance the camera is from the scene's action.
- Incorrect. What is visible from the camera can impact the speed of a rendering, but it is typically not a limiting factor.
- The number of colors used for the scene's models.
- Incorrect. The number of colors used typically has no impact on the speed of rendering.
- The size of the triangles in the models.
- Incorrect. The physical size of individual triangles changes depending on the distance between an object and the camera. We typically don't worry about the triangle sizes.
-
Q-89: You are modeling a fish that has 3 fins, one on either side of its body and its tail fin.
You want to animate the fish to simulate its swimming through water. How many models should you create?
- 4
- Correct. Model the fish's body and then each individual fin.
- 1
- Incorrect. If you model the entire fish as a single model, you will not be able to move the fins independently of the fish's body.
- 3
- Incorrect. Three models for the fins, but what about the body of the fish?
- 9
- Incorrect. How did you get 9?