Hello, I try to interpole a spline Surface. I have a grid of N*M points. I need to compute (N-1)*(M-1) spline patchs. I impose that these patchs are udegree=vdegree=3. So a patch equation is like that : a + bu + cu*u + d*u*u*u + v*(e + fu + gu*u + h*u*u*u) + v*v*(i + ju + ku*u + l*u*u*u) + v*v*v*(m + nu + ou*u + p*u*u*u) 16 unknow parameters to get. I can get, for each point, the utan, and vtan. I also know the value on uvtan on the 4 corners of the whole surface. Now, what I need is the uvtan on each point. If I have that, for each patch, I will have 16 equations, and it will be perfect to finish computing the surface patch per patch. Actually, with points, utan, and vtan, I have only 12. I think the missing constraints are, if P is a patch, and Q its right patch, Puv(1,0) = Quv(0,0) and Puv(1,1) = Quv(0,1) (assuming all patch have urange=vrange = 0..1) But anyway, I don't manage to make a matrix to compute all my uvtan. I bet the matrix will be width = height = M*N, but if I could have a smallest matrix, or astuces to inverse it faster, it should be better. If someone can give me clues to get my uvtan, it should help me a lot ! Thank you ! * sorry for my english, this is not my main language...