>>1899868It looks like a multi vehicle Chinese Postman problem. Geometric distance isn't quite the right thing to minimize because a u turn costs more than a right turn costs more than going straight. How do I translate a turn angle into extra distance?
Hills and wind are also considerations. It's probably safer to go down the steep paved hill and up the gradual gravel path in pic related. It also happens to be the direction with right turns. The other way might be faster because then you don't have to brake as much at the narrow trailhead at bottom of the hill.
Customizing the solution for a single vehicle (one day's tour) could include disallowing certain edges to be duplicated, adding constraints on how the odd degree nodes (tees or forks) are paired up, changing the direction of cycles and possibly including the constraints that a pair of edges must be in a cycle. I don't think the last one works in general but I picture Hierholzer's algorithm piecing together the smallest cycles that contain specified edges. The last is unclear to me. If you have two bridges upstream of the waterfall and two downstream, you can't reverse just an upstream and a downstream bridge crossing together, unless there's also two ways over the cliff on each side of the river. Or the two ways over the cliff might be a single way you're willing to do twice.
