From this exercise and the following lines: vector4 o = dihedral({0, 0, 1}, @P); // align z-axis with @P vector We get this result: Now we want to face her ass out, which means we gotta rotate her 90-degrees on her y-axis. From this exercise, we learned how to build a quarternion from a rotation and an axis. vector4 r = quaternion(set(0, radians(90), 0)); // e.g {0, 90, 0} - rotate y 90-deg We combine both the rotations by multiplying the quarternions, using qmultiply:

How Houdini determines orientation Houdini searches for these attributes, in this order. It goes down this list until none is found. @orient attribute. Use this to orient copy/instances. Using @N as the Z-axis and +Y is up. Use @v e.g. velocity. If @rot exists, apply it to the above. Copy to Points We have a point with @N = {0, 1, 0} e.g. its normal pointing up (the yellow trail).