<a href="https://en.wikipedia.org/wiki/curvilinear_grid" class="extiw" title="en:curvilinear grid">en:curvilinear_grid</a> by <a href="https://en.wikipedia.org/wiki/bilinear_interpolation" class="extiw" title="en:bilinear interpolation">en:bilinear interpolation</a>, example on a quarter symmetry model with a circular interior and square exterior
Tom Ruen
<span class="int-own-work" lang="en">Own work</span>