Polar cap shape for oblate and prolate stars with oblateness parameter a/R = {0, 0.5, 1} in blue, green, and red, respectively. The black dashed line shows the reference solution for the Deutsch field as a check. The obliquity from the left column to the right column is χ = {0°, 30°, 60°, 90°}. The first row is for an oblate star with one mode ℓ = 1, the second row is for a spherical dipole magnetic field at the surface, the third row is for a prolate star with one mode ℓ = 1, and the fourth row is for a spherical dipole magnetic field at the surface.