In this case, the reference point seems to be at the origin of the coordinates of the world, but I want to get the length of the path that is sampled here:
You can capture the length of the spline with
Sample Curve by passing the spline length provided by
Spline Parameter as Value.
This looks like this:
PS: If you use a NURBS curve, you would have to convert it at the very beginning with the node
Resample Curve, otherwise you would always get the interpolated values inherent to the NURBS curve.