Guys, not to be a downer or anything, the track day apps that have this feature ask users to run the couse in the slowest speed possible, and to get really good acuracy it needs to be on foot, or with some aditional gps signal booster.
My home track has 20+ users of the app and still after 2-3 years its not perfect.
Iphone/android have around 1hz capture, while good gps signal enhancers go from 5-20 and top of the line ones (thousands of usd) can capture up to 100.
It will take lots of dedication and re-runs to get a good/great track in.
Having said that, i am looking foward to this feature.