Hi,

In this file, I have a given spline, which is fixed and the tangent at the origin.

(Btw, I am wondering why I can fix the tangent at origin : if the spline is fixed, the tangent at any point too, but it's not the matter of my post)

I want to define a segment, being tangent at the origin.

So, I draw a segment, one point at origin, the other free, and I define a tangent property.

And I get what is on my screen.

How can I build this totally elementary construction ?

OK, I can declare some colinearity with the tangent of the spline.

But this kind of behaviour is surely totally normal ?

What do you mean by "I have a given spline, which is fixed and the tangent at the origin"? Do you want the spline to be tangent to a line that passes through the origin and is vertical?

If that is the case, see attached file.