Then I know how to solve this problem. Was an equation provided or are you supposed to figure it out yourself? Now, granted, I bet there is a way to calculate the surface normals without an exact equation, I just don't know how. Check out this link:
Normal Vector -- from Wolfram MathWorld
Basically, this says that the normal vector at any point is:
They just denote the partial derivite of . What that basically means is that if, lets just say for example, we had a grid with the following equation:
Then to find you just take the derivite with respect to x, and let y act as a constant. To find you let x act as a constant, so:
Does that make sense?