Calculating normals between 2 meshes ending up in seams

Question

My Task

I currently creating a terrain for Unity3D which is specialized for mobile-devices with low memory for a running app. Allowing a terrain with a size of 15.

Answer 1

I still don't know why it happens but when replacing this....

Vector3 u = vertices[item.Face1] - vertices[item.Face0];
Vector3 v = vertices[item.Face2] - vertices[item.Face0];

Vector3 fn = new Vector3((u.Y * v.Z) - (u.Z * v.Y), (u.Z * v.X) - (u.X * v.Z), (u.X * v.Y) - (u.Y * v.X));
fn.Normalize();
normal += fn;

with another AddFaceNormal-method it works. I don't know why this happend but now it works.