Create a GPS/GPX alert app if off-track

Dear all,

I like to propose a track for the GPS system.

If I’m hiking, I mainly use OSMand from the f-droid store.

To find my way, I use a GPX-track without active routing.

I’m simply follow the line.

I’m searching for an app, which will alert me, if I leave the track.

Maybe there is a programmer in the forum, who like to help?

Thank you very much!

Kind regards

Piet