Problem in dividing the mid-plane in multiple area(or planes)
 

Hello firends,
I faced problem when i was trying to divide the mid-plane into multiple areas(planes) . My mid-plane is a tilted surface inclined with x, y and z axis at an angle. I tried doing this with surface bounded with three points but failed. I am also posting a picture of my surface. I request if anyone can suggest some other technique to do so the same.