Buzz’s Blog: On Web 3.0 and the Semantic Web

May 24 2011   10:37PM GMT

Straight line 3D modeling with polygons, part 3

Roger King Roger King Profile: Roger King

Please note that you can also read this blog entry on the website I maintain for my animation students at the University of Colorado in Boulder:

I have not posted to this blog for over 2 weeks because I was in Chile having a great time. But I am back now.

Creating 3D models with Autodesk Maya.

In five recent postings, (12345), we looked at the simple, powerful mathematical techniques that underly the specification of curved lines in 3D graphics and how they are used to create 3D models.

In the last two postings (67), we turned to straight lines, and how 3D models can be built entirely out of 2D straight lines, using polygons.  We also looked at the minimal information a graphics or animation application must manage in order to unambiguously represent a 3D object created with straight line geometry – and we saw that it isn’t very complicated at all.

Manipulating a 3D object.

Today, we begin to look at the process of molding a 3D model out of basic 3D objects provided by most 3D modeling and/or animation applications.

Recently, I went to Rapa Nui, also known as Easter Island, which is a five hour ride on a jetliner from the coast of Chile.  Over a period of several hundred years, dating back to about the year 1000, the indigenous inhabitants of the island created giant stone statues called Moia.  They consist of heads or upper bodies (including heads), and for the most part are flat in the back.  Here is a photo of a few of them, taken from

On my way back from Chile, I hunkered down in my coach seat with my 17 inch Macbook Pro and created a model of one.

A Moai model created with Autodesk Maya.

Consider the following image, which is the beginnings of the Moai’s face.  It is a cylinder with its back sliced off flat, and the bottom of it pulled out to make the chin:

I created this by selecting the bottom semi-circle of the sliced cylinder and pulling it outward.

That’s the first lesson:

We can craft a model by dragging vertices, edges, or faces of polygon obects.

The next thing I wanted to do was to pull the nose out of the face.

Here is our second lesson:

When taking a Maya primitive (in this case, a cylinder) and crafting a model with it, you create detailed geometry when and only when you need it.

Consider this image:

You see that I inserted what is called an “edge loop” that adds geometry about 2/3 of the way down the face.  It is in orange in the image above.  This is what will become our nose.

More next time…

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