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:
   $(-x+1.2a)^{1.7}+(y-b)^2 < r^2$