If sturm doesn't work, try rotating or translating the shape by some small amount. See the sub-directory math in the scene files directory for examples of polys in scenes. There are really so many different quartic shapes, we can't even begin to list or describe them all. Note that you do not confuse quaDRic with quaRTic . A quadric is a 2nd order polynomial while a quartic is 4th order.
Quadrics render much faster and are less error-prone.
J will give different shapes. If you take any three dimensional point and use its x, y and z coordinates in the above equation the answer will be 0 if the point is on the surface of the object. The answer will be negative if the point is inside the object and positive if the point is outside the object. The easiest way to use these shapes is to include the standard file shapes.inc into your program. Don't confuse radius with width.