Computer art for the Tektronix 4052. (part 6) Joe Jacobson.

This month I will describe a polar coordinate program that is completely different from those I have presented in past issues of Creative Computing. This is the Wobbly Spiral program. The name follows directly from the algorithm.

The program draws an exponential spiral that has a sine wave superimposed on it. The "tightness" of the spiral is controlled by the parameter L. The amplitude and frequency of the sine wave are controlled by the parameters C, E, and K. All these constants are entered from the keyboard, following user prompts.

The sine wave amplitude has a constant component (E) and a component (C) that decays exponentially with angle. (If you want the wobble to be the same size everywhere along the spiral, set C equal to 0. Otherwise, the wobble will decrease in size from the center of the spiral to the outer edge.) The parameter G is the angular increment used in computing the curve.

If you set T1=1, you will get a plot of the wobbly spiral with a list of input parameter values at the bottom of the picture. If you like the picture, make a hardcopy print for future reference. Then clear the screen and hit RETURN and you will get a "clean" plot (without the parameter list) of the same picture. Then you can make a hardcopy to show your friends. If you don't want a parameter value list at all enter 2 after the prompt to enter T1.

If you want an overlay, yielding inter-twining sine waves along the spiral, set P equal to 2. Otherwise, use P=1. Table 1 lists suggested ranges of values for all of the input parameters.