For simple 3-d spirals, a third variable, h (height), is also a continuous, monotonic function of θ. For example, a conic helix may be defined as a spiral on a conic surface, with the distance to the apex an exponential function of θ.
The helix and vortex can be viewed as a kind of three-dimensional spiral.
For a helix with thickness, see spring (math).
Another kind of spiral is a conic spiral along a circle. This spiral is formed along the surface of a cone whose axis is bent and restricted to a circle:
This image is reminiscent of a Ouroboros symbol and could be mistaken for a torus with a continuously-increasing diameter:
Read more about this topic: Spiral
Other articles related to "spiral":
... A spherical spiral (rhumb line or loxodrome, left picture) is the curve on a sphere traced by a ship traveling from one pole to the other while keeping a fixed angle (unequal to 0° and to 90 ... The gap between the curves of an Archimedean spiral (right picture) remains constant as the radius changes and hence is not a rhumb line ...