Is there a way to flip the orientation of certain curves in Geometry Nodes?

Question

I have a mesh with multiple islands that I have converted to curves. I am now trying to apply a profile to these certain "curve islands" but it seems like there are edges with orientations that are flipped. Is there a way to selectively reverse these edges so that the profile has correct normals?

Currently reversing the curve at certain indexes seems to work but it isn't consistent and flipping faces doesn't seem to do anything.

Blend File

Answer 1

This answer is based on the solution shown here:
How to correct curve tilt, tangents and normals of a curve?

However, your question is only about recognizing the orientation of the tangents in order to deduce which curves need to be reversed, which is why I am only applying part of this solution here.

The principle is simple:

1. You first determine the direction from the center of each spline to each point of the spline.
2. If you then generate the cross product of the tangent of the curve points and this direction, and generate the dot product with $(0,0,1)$ or $(0,0,-1)$, this resulting value is either positive or negative per point. However, you need to capture this value with Capture Attribute in the point domain!
3. If you then plug this value directly into the input Selection of the node Reverse Curve, it will be interpolated from the Point domain to the Spline domain, and used as a boolean value. This way the alignment of your curves is consistent throughout.

_{(Blender 3.2+)}