Quote:

> Does anybody know the calculation for drawing a spiral?

> and or

> The calculation for drawing a double helix?

Sure. What kind of spiral? The key to doing this is to use polar

(or cylindrical, for the

helix) coordinates and to make the coordinates themselves a function of,

say, t. The double helix is almost trivial -- the radius stays constant

(independent of t), while the angle

and z component are both proportional to t. Start the two spirals on

opposite ends of the

circle (by giving one angle an offset of 180 deg). By varying the ratio

of the proportionality constants between angle and Z, you'll get a

"tighter" or "looser" double

helix.

The spiral simply relaxes the requirement that the radius is

constant. It also becomes

a function (up to you to decide WHAT function) of t.

Bob Schor

Pascal Enthusiast