I have some question about Non-Planar geometry 1. What is non planar geometry? 2. Why this happens after rendering?

Why did I get this line in the middle and the shading is different.

enter image description here

  • $\begingroup$ Please clarify "Why this happens after rendering?" What is happening after the render? $\endgroup$ – Leander Jun 5 '18 at 7:18
  • $\begingroup$ @Leander I've added a picture of that. $\endgroup$ – Abhinay Singh Negi Jun 5 '18 at 7:21