As you see the perpendicular frame of a 3d curve has x-y direction not parallel to global one
How this x-y direction is defined?
Can I align these directions to global one (in top view) without rotating the curve (keep the curve untouched)?
Or, how can I measure the angle between the two x-directions in top view?
If you supply your GH file it would help a lot. I believe the x-y orientation of the plane is defined by the torsion of the curve. You can rotate them back to how you want them in a few ways. You just need to find a way to orient the appropriate axis (either x or y in this case), and maintain the same z-axis.
Thank you, TheCyclist, for your suggestion!