title: How to interpolate using in polar coordinate
body: <p>I have polar coordinates, radius <code>0.05 &lt;= r &lt;= 1</code> and <code>0 ≤ θ ≤ 2π</code>. The radius <code>r</code> is 50 values between 0.05 to 1, and polar angle θ is 24 values between 0 to 2π. </p>
  
  <p>How do I interpolate <code>r = 0.075</code> and <code>theta = pi/8</code>?</p>