As it is about consuming path: how about the pedestrian routers - Certainly, they will have to control for mtb:scale just the same? The grade 1 perhaps, grade 2 certainly not wanted for Sunday strolls? Pictures here resemble SAC mountain_hiking/demanding_mountain_hiking.
I think some mapping between MTB:scale to sac_scale and then consuming sac_scale is advisable. The wiki: Key:mtb:scale - OpenStreetMap Wiki says mtb:scale=5 is T4 (alpine_hiking) (or higher, though I doubt it, previously there was “higher” sign, I put in “equal or higher” but maybe it should be “equal”), mtb:scale=6 is said to be T5 or T6 (demanding and difficult alpine_hiking).
I would think the correspondence is like this:
mtb:scale=0/1 equals to sac_scale=hiking
mtb:scale=2/3 equals to sac_scale=mountain_hiking
mtb:scale=4 equals to sac_scale=demanding_mountain_hiking
mtb:scale=5 equals to sac_scale=alpine_hiking
mtb:scale=6 equals to sac_scale=demaning_alpine_hiking/difficult_alpine_hiking
It is quite common to have a section of trail that is relatively easy to hike, but very difficult to mountain bike oo so it is not have a conversion chart between sac_scale and mtb:scale
A nice catch on the graphhopper issue tracker mentions stairs. They grade as S2 in the mtb:scale documentation (linked above). Indeed, steps are mentioned there, the German version even says “Stufen und flache Treppen” (steps and flat stairs – anything between 20% and 45% decline according to construction standards) - With full suspension, stairs are easy to mountain-bike (down), much easier than the blocky terrain shown in the example picture of grade 2. There it talks about up to 70% steep steps (Absätze in German). But that is how it is documented. If it were not for the German word Treppen, I’d not read the term steps as meaning something constructed, would you?
Radius of curves something that also comes to mind, where walking and cycling clearly have different difficulties. What more?
I see this the same: It is not about defining defaults, instead it is about adding detail to the mappings.
Maybe editor presets to the rescue? They might pull in a number of keys, that mappers probably would never consider relevant for what they are about to map. Smoothness on a hiking path, mtb:scale probably not mapped by walkers But useful for users?
Pondering some such “presets”
Sunday stroll
Trail run workout
Demanding mountain hike
Actually, I see that a bit duty of consumers, to come up with a list, what attributes they want, whether to render or to route something? Or can the OSM community guide them?
Depends on how steep they are, but in any event, riding up steps can be very difficult. The difficulty increases with the number of steps, and how steep they are.
I don’t think the difficulty of mountain biking a trail can be relied on to give an indication of the difficulty of walking or running it (and vise versa). For one thing, multiple obstacles in quick succession multiply the difficulty of mountain biking as cleaning the first obstacle may put you in a bad position to attack the second, and so on. A specific case is a drop (i.e. a step down), followed immeadiately by a turn. If the turn wasn’t there you could use momentum to get over the step easily, but the turn means you have to reduce speed.
Well, the use case is not to render sac_scale based on mtb:scale but rather deciding not to route over or render a path based on them to avoid sending people to potentially difficult terrain. So it is not about assuming something is the case (“mtb:scale X means some concrete hiking difficulty”) but about the opposite (”based on sac_scale, this is probably not easily passable on a bike”). So the debate is more if it is appropriate to recommend consumers to make guesses when better data is not available. The main use case would be ignoring difficult hiking paths for bike-centric applications not designed specifically for mountain bikes but rather for a general purpose bikes/bike-touring etc.
For such applications, I think it is a good idea to ignore/render as impassable definitely anything with sac_scale over alpine hiking and possibly anything above hiking (assuming designation and access is unknown).
On the other hand, for applications that try to avoid difficult trails (anything above hiking), it makes sense to ignore paths with mtb:scale over 4.
There will be some false positives but overall I think it would lead to better results for the user. For actual mapping, somebody needs to survey and people should be encouraged to fill in missing info. However, I as a hiker do not feel comfortable putting in mtb:scale, especially for trails that do not seem to be used by bikes at all.
There is at least one router of the three available on the openstreetmap website that does exactly that. According to what they say, for 15 years now. They should be applauded
That is the topic here. I did a bit of overpass and found, that indeed, to know for certain, one has to visit the location! Then I did a bit of statistics, base recipe here - ohsome - dashboard - change mtb:scale to higher number and/or change area of interest. I’d set the threshold at 2 at least most (at 1 hiking is on par with mountain_hiking, at 2 it is dwarfed by mountain_hiking.) BTW: That there is so much remainder says, that indeed the gap to fill is substantial.
But useful for users?