(sorry for the delay as we are just back from vacation)
you should use fTPx as it is a kalman-filtered version of the VP that is also converted to standardized coordinates (independent of camera resolution). So you can just use it as the filtered (smoothed) VP location, with the following conventions:
-1000.0 is at the left edge of the image / field of view
0.0 is dead center
1000.0 is at the right edge of the image / field of view
Given the clearly maked black/white lines at the center of the road in your competition, it might be interesting to also try some line detection code? We have not yet implemented any on JeVois but a google search for "visual line following" returns results that might interest you to program your own JeVois module.