# Is there a source/cookbook of equations that approximate geometric shapes?

I'm numerically modelling flows around various geometric 2D shapes. Is there a good source/cookbook of equations that approximate these? Some examples are

1. Rectangle: $$(x-a)^n+(y-b)^n < r^n$$ where $$r$$ is side length and $$n$$ is even. The larger $$n$$, the sharper the corners. Also e.g. $$\text{max}(500 |x-a|, 55 |y-b|) < r^2$$ achieves this .
2. Tilted square: $$|x-a|+|y-b| < r^2$$
3. Bullet: $$(-x+1.2a)^{1.7}+(y-b)^2 < r^2$$