Report- Modelling

Creating 3D models in Maya is a unique and evolving art form that requires the understanding of many disciplines including form, anatomy and mechanics.
While Maya supports 3 surface types – NURBS, Polygons, and Subdivisions. This report will focus on aspects of Polygon modelling.

© 2012 Jimi Green

Polygon models are versatile, intuitive to model with and are well suited to hard surface and organic forms. They are the most common surface type used in the film industry and are the ‘backbone’ of all game art (McKinley, M 2005, p13).

A polygon ‘mesh’ is constructed using flat faces that share edges and vertices. A standard workflow is to create a low resolution or ‘proxy’ model for ease of UV layout, rigging and animation, then to ‘smooth’ the model toward the end of the project, whereby the geometry is subdivided to the level required. Each level of subdivision quadruples the number of poly faces (Palamar, T, Keller, E,  2011). Faces with 4 vertices are known as ‘quads’. It is best practice to keep models to quads wherever possible as four-sided faces respond well to subdivision and deformation. 3 sided faces (tris) and n-gons (faces with 5 sides or more) tend to cause pinching in the model (Miller, E 2008).

© 2012 Jimi Green

There are some limitations, boundaries and rules an artist must be aware of.

Polycount – your software/hardware combination is only capable of displaying a finite number of polygons. As ‘polycount’ increases, the computers ability to process and display them reduces exponentially. Careful planning is required to only increase the density of polygons where and when it is necessary (Miller, E 2008).

Geometry To Avoid

© 2012 Jimi Green

Non-planar – It is best to keep all vertices of a face along a single plane. If a vertex is moved off that plane, it becomes a ‘twisted’ or ‘bent’.

‘Lamina’ – where faces share all their edges- in other words one or more faces are directly on top of each other.

Non-Manifold

© 2012 Jimi Green

where a third polygon is extruded from a shared edge or

where two polygons share a single vertex (bow tie)

© 2012 Jimi Green

The above problems can be remedied with the ‘cleanup’ command which will delete the bad geometry.

Non-conformed Normals – normals determine which side of the surface will face the camera for rendering.

© 2012 Jimi Green

Correct normals appear like the above, facing in the same direction.

© 2012 Jimi Green

this next example (with normals displayed and without) has some faces pointing in toward the model.

The remedy is to select all the faces pointing the wrong way and apply the ‘reverse normals’ command (Palamar, T, Keller, E,  2011).

Tools-

An advantage of poly modelling is that very few tools are required. Some of the most used include:

© 2012 Jimi Green

Split polygon– probably the most simple and widely used of all the tools, it creates a split through a one or more face(s) to add geometry.

© 2012 Jimi Green

Insert edge loop – allows you to select and then split the polygon faces across either a full or partial ‘edge ring’ on a polygonal mesh.

© 2012 Jimi Green

Extrude – Pulls new polygons out from existing faces, edges, or vertices. (Autodesk Maya 2013)

Techniques and workflow

While the tools are relatively simple, an understanding of what you are building is perhaps the most important aspect of any kind of 3D modelling. If you are building a complex mechanical form, then it is important to know its function, form and how it works. Are the forms smooth or hard-edged and to what degree?

If the form is human or another living creature then you need to know how the masses make up the form. The first step should be sketching and research to solve these questions. Giovani Nakpil suggests the next stage should be modelling in clay as ‘touching something tangible’ helps to figure out how the masses interact with each other, the rhythm and movement of the forms. (Dacol Jr, C, Van Beek J, Nakpil, G, 2009)

‘Image planes’ allow importing of orthographic reference into Maya before building. This, combined with the ‘box modelling’ method – starting with a poly primitive and shaping and extruding limbs and other body parts, is a common technique.

© 2012 Jimi Green

© 2012 Jimi Green

If the character is symmetrical, only half the model needs to be created.

© 2012 Jimi Green

Then duplicate the model and scale to -1 in x

© 2012 Jimi Green

Use the ‘combine’ command to form one mesh.

© 2012 Jimi Green

Then most importantly – marque-select all the overlapping vertices and use the ‘merge vertices’ command. This ensures proper geometry.

The results from this box modelling method can be quite pleasing, however they will not necessarily be adequate for deformation under animation controls. The model will benefit from ‘retopology’ or changing the ‘edge flow’ of the geometry, based on the regions and divisions of the body, emphasizing the relationship between the various structures (Miller, E 2008).

References:

McKinley, M 2005, ‘The Game Artist’s Guide to Maya’, Sybex, San Francisco

Palamar, T, Keller, E,  2011, ‘Mastering Autodesk Maya 2012’, Wiley, Indiana

Dacol Jr, C, Van Beek J, Nakpil, G, 2009, ‘Character Modelling 3’, Ballastic, Adelaide

Miller, E 2008, ‘Autodesk Maya Techniques- Hyper-Realistic Creature Creation’, Autodesk, CA

(Autodesk Maya 2013) Autodesk Maya 2013 onscreen help menu.

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