Feeding trajectory points to a SMC controller for vehicle lateral control

I have developed SMC controller for lateral movement of vehicle with help of some research papers and few books. All the math is done and its ready in MATLAB. The problem is how do I give/ feed desired coordinates to the controller (X,Y,psi)? Currently I am feeding time based coordinates using Signal Builder and it works well but its not the way and I am facing chattering issue due to (may be) wrong method of implementation. In paper they have got good results and I have made SMC with few improvements. Is there any perticular method (I have read B-splines, G2 splines, pls explain) for feeding desired coordinates based on vehicle position? I m not asking about path planning (its done) but how to feed those points to a controller, or any methods or codes. Thanx a lot in advance.