Circle surface becomes less round when boolean unioned with another surface

I have a circle surface and another complex polysurface. When I boolean union the two surfaces the circular part shows that it has edges, as opposed to a perfectly round circle. Before the union the circular surface was perfectly round. What’s the reason for this and is there a way to do anything about it?

It’s just the render mesh, presumably. Your surface is fine.

Thank you Jim

Sorry I was typing on my phone and couldn’t elaborate, but what would have happened was that the render mesh for your boolean result was rougher-looking than for the original object. I’m not sure how that’s possible, since booleaning will always increase the polygon count, but I suppose if the original was a simple cylinder it wouldn’t have many edges showing how “rough” the render mesh can really be. See