Should I set control upvectors?

For most people the answer is “no”.  Control upvectors are only needed if your track is flipping upside down.  They give you a way to control which way is up.

You can find the T vector by finding a normalised vector between two points on the centreline.

1. If your path is planar in the xz plane, you can construct the rest of your TNB frame as

• N = T x y
• B = y

2. If your path is non-planar, but not flipping upside down, you can construct the rest of your TNB frame as

• N = T x y
• B = N x T

3. If your path if flipping upside down, you need more control over what is “up”.  Use the control upvectors to interpolate B.  Then you can construct the rest of your TNB frame as

• N = T x B

High