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Tutorial: Making Ganglia

It’s finally time to put all this polygon theory to work. In this tutorial, we'll use Polygon Extrusion to create a nerve cell, called a ganglia (see Figure 7.23).

Figure 7.23 Completed, rendered ganglia.

1. Start with an Icosahedron.

Draw a wavy curve in the Front view, starting at the origin and heading up in positive Y. Use a B-spline for easy control.

Now get a primitive icosahedron and leave it at the global center where it came into existence. (see Figure 7.24).

Figure 7.24 The icosahedron and the extrusion path.

Switch to POL (polygon mode) and select four of the faces with the G supra key, making sure that you choose non-contiguous (not touching) faces (see Figure 7.25).

Figure 7.25 The icosahedron with four faces selected, showing the centers.

When non-contiguous polygons are selected, each one gets a local center with the Y axis oriented along the normal of the polygon. We'll use this local center as a local coordinate system to extrude each polygon in a different direction.

2. Extrude Some Arms.

With the icosahedron selected, bring up the Extrusion dialog box, and see that the On Curve option is the only option available. Click Ok and then pick the extrusion path you drew to complete the command. Arms should sprout from the selected faces of the icosahedron (see Figure 7.26).

Figure 7.26 The icosahedron with straight extruded arms.

3. Set the Transform Options.

Undo the last command by holding the U Supra key and clicking anywhere with the left mouse button, until the arms go away. Now invoke the Surface->Extrusion dialog again. This time turn on Curve Placement and click the Transform button to show the transformation options (see Figure 7.27).

Figure 7.27 The Extrusion Transformations dialog, set for the ganglia.

Set the Scale in X, Y, and Z to 0.8, which makes each successive polygon 10 percent smaller than the last.

Set the Rotation in Y to 15 degrees, which makes the arms twist around the direction of the normal as they move out.

Close the dialog, and execute the command to create the armed ganglia (see Figure 7.28).

Figure 7.28 The ganglia with spiral arms.

As you can see, extruding polygons can yield some interesting results. Extruding polygons along a path is usefull for making fingers on low-poly hands, and also for other path extrusion effects like tree branches and roads. As an extra bonus, being able to transform a polygon at each stage of the extrusion adds in functionality like that found in the repetitive duplication tools. Use your imagination and explore!


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