[Math] How to calculate the bounds of a square within a circle with known radius

geometry

Given these information:

Graphical representation of the shapes

  • Top-left coordinates of the green square, (0, 0)
  • Center coordinates, (x, y)
  • Length of the green square, L
  • Radius of the blue circle, r (which basically just L / 2)

Is there a way to calculate the bounds (top-left, top-right, bottom-right, and bottom-left) coordinates of the red square?

Best Answer

Consider the following picture.

Useful line segments indicated

Line segment $a$ has length $\frac{L}2$. Therefore, line segment $b$ also has length $\frac{L}2$ (they are both radii of the blue circle). Therefore, in the triangle $bcd$ we see that $c$ and $d$ both have length $\frac{L}{2\sqrt{2}}$.

Now the center has coordinates $\left(\frac{L}2, \frac{L}2\right)$. This means that the corner coordinates are $\left( \frac{L}2 \pm \frac{L}{2\sqrt{2}}, \frac{L}2 \pm \frac{L}{2\sqrt{2}}\right)$.