# How to use Monotone cubic interpolation in 3D?

I wanted to use Monotone cubic interpolation, but the site only provide explanation for 2D case. How can I extend it to 3D?

• Do you mean that you have a set of 3D control points, C0, C1...Cn, and, I assume, some rotation matrix, P, such that, (P.Ci) [x] is strictly increasing, as are (P.Ci) [y] and (P.Ci) [z] ? Commented Apr 24, 2017 at 11:56
• No, i mean in 3D a point is defined by (x, y, z) instead of (x, y). Commented Apr 24, 2017 at 12:04
• Your question is ambiguous as you don't specify monotonic in relation to what in 3D? Commented Apr 25, 2017 at 13:10
• @JarkkoL You need to check the link that I provided. Commented Apr 25, 2017 at 15:27
• It doesn't disambiguate how you want the function to be monotonic in 3D. If you want the function to be monotonic along y-axis like in the 2D case, it's trivial extension, but if you want it to be monotonic along each axis, it's different. So which is it? Please clarify your question. Commented Apr 25, 2017 at 15:58