用maya制造环形跑道模型和材质（英文）

(23) Use the Wire Tool and make sure you increase the dropoff distance so that the tool actually has an effect. Modify the the two curves by raising and lowering the points, remember not to stray too near the end points or you may result in polygons displacing too much. One good way is using the side or front views to modify so you can see the smoothness of the curve.

　　

　　(24) To create the run off areas – usually in the form of sand traps on most race circuits, you can either extrude the edge of the polygons, or go back to the original NURBs and offset a further distance. It doesn’t matter if the shape seems weird as you can trim down the polygons later. This technique will already have the UVs in place so you could create a nice raked effect.

　　

(25) Most racetracks have some kind of armco barrier system. The best way to handle this is to create a perfect set of barriers from your original NURBs curves and tweak their positioning later. You may need to rebuild the smaller sections that you originally smoothed out to have less spans so they match the 32 spans in the 128m sections. Using the curves you can extrude polygon surfaces.

　　

　　(26) Combine all the barrier polygons, an apply a front barrier shader group to them with repeats set to 16 U, and 3 V. Then duplicate the polygons and reverse the normals and apply a rear barrier shader group with the same settings. Barriers should now snake around the track.

　　

(27) Now you have created the most complex part, you can fill in the gaps. You can either build the polys seperately using Append to Polygon, or perhaps extrude edges. Or on a larger scale use tools like the Fill Tool found in the Edit Polygons menu to fill large holes which you can split up or triangulate so you can sculpt the polys by moving around the poly components.