Build an orient Attribute for Copy to Points

What it does

Computes a rotation that takes a chosen up vector onto each point normal and stores it as a quaternion in @orient. Copy to Points reads @orient automatically, so every copy is aimed along @N.

When to use it

Use it whenever copies need to follow the surface - grass and fur along normals, panels on a hull, arrows along a flow. Driving orientation with @orient avoids the gimbal and flipping problems you get from feeding @N and @up loosely.

The VEX code

// Aim each point's up vector along its normal; copies read p@orient.
vector up = {0, 1, 0};
matrix3 m = dihedral(up, normalize(@N));
p@orient = quaternion(m);

Inputs and assumptions

• Points with a normal @N (add a Normal SOP or compute it first).
• @orient is a vector4 quaternion; the p@ prefix declares it correctly.
• Runs on the target points, before Copy to Points.

Common mistakes

• No @N on the points, so dihedral has nothing to aim at - compute normals first.
• Not normalising @N; dihedral expects unit vectors.
• Declaring @orient as the wrong type - it must be a vector4 (p@orient), not a vector.
• Also feeding @N/@up to Copy to Points at the same time; let @orient own the rotation to avoid conflicts.

Frequently asked questions

What attribute rotates copy to points?

A vector4 quaternion named @orient. Copy to Points reads it automatically and uses it as each copy rotation, which is more robust than @N and @up alone.

What does dihedral do?

dihedral returns the shortest rotation that takes one vector onto another - here, taking the up vector onto the point normal so copies aim along the surface.

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