We can render a 3d hexagon height map by using the dual graph, which is a triangle grid formed around each hexagon corner. The three hexagons touching a corner form a triangle. Push the slider up to see elevation added in.
I sort the triangles by their row value so that the rendering is back to front — https://en.wikipedia.org/wiki/Painter%27s_algorithm — maybe there are some occasional glitches.
Another way to make hexagons 3d is to keep the tops flat, and then draw sides on them: