Spline tracing/detection/collision

Hello , I need help.
So I am create Actor based on Spline component.It is generate spline mesh :

My Character must move on spline.
The problem is that I should get the distance along spline of the point at which the movement begins.
Firstly spline component dont tracing and dont reacts on collision/hit
Secondly i cant get distance along spline from vector.

Sorry my English.Have Ue4 Solutions of this problems?

Using the spline variable you should be able to return a world location from a certain “distance along spline”

or are you trying to do the opposite and find a position on the spline from something not currently on it?

I am trying to do the opposite and find a position on the spline from something not currently on it.I want trace down from my character.Then get location of hit by spline.Then from location of hit get distance along spline.
I demonstarate what i need in pic.

I am also interested into this. Any idea how to do it?

Cheers,