Math thing that currently interests me...
Suppose you had 2D parametric function
x(t), y(t)
with the property that differential vector is always a unit vector
| x'(t), y'(t) | = 1
You then convert that to polar coordinates
r'(t), φ'(t)
Since r'(t) is always 1, it can be dismissed, and φ'(t) alone describes the traced shape.
Problem: Given φ'(t), how to find the original 2D shape?
Analogy: Find the position of a car moving at constant speed, given the steering wheel angle over time.