[mkgmap-dev] unpaved roadsFrom Gerd Petermann GPetermann_muenchen at hotmail.com on Thu Feb 23 07:31:41 GMT 2017
Hi Greg, as you said we have to live with the limitations of the Garmin img format and the routing algo. My understanding is that the default style should produce reasonable results for correct input data. If I got you right you'd like to have some user interface (maybe sliders in a GUI) to express your preferences of different road types or surface types and that should be used to "fine tune" the values for road_speed, road_class, and the unpaved flag so that one doesn't have to understand all the complex rules? Gerd ________________________________________ Von: Greg Troxel <gdt at lexort.com> Gesendet: Mittwoch, 22. Februar 2017 15:42 An: Gerd Petermann Cc: Greg Troxel Betreff: Re: AW: [mkgmap-dev] unpaved roads [you didn't copy the list. if you want me to post this I'm happy to.] Gerd Petermann <GPetermann_muenchen at hotmail.com> writes: > okay, a bit late. understood. I didn't mean to complain, just to offer a perspective that I thought might be helpful. > The default style was already changed to set the unpaved flag in the > same way as the surface wiki suggests. Arguably that is the most reasonable default. > I agree that this is just one of many ways to use the flag, but I have > no idea what you try to describe with the part following "try to map > some utility function ..." . What I meant is that a routing user will have an opinion about the usefulness/goodness of any route based on many things. Right now there is a strong bias towards "shortest distance" and "fastest time" in the routing world and "least fuel" is starting to show up. I probably should not have said "utility function". That's a concept from economics which assigns a numerical value to a situation, and there's an assumption that a rational actor seeks to maximize utility. https://en.wikipedia.org/wiki/Utility This concept acknowledges lots of complexity. A car that works but is not fancy might be worth 100 points and one that is just as useful but looks nicer 120, to one person. Or 200 to someone who sees it as jewelry/status, or 90 to someone who finds the niceness pointless and then worries about damage. What I was getting at is that for a route, one can think of each segment as having a cost (which is sort of inverse utility), where the cost is about how the route user feels about it. Here, the cost function encodes how one feels about surface types, speeds, distance, congestion, traffic lights, left turns, etc. Then, I was suggesting that optimal routing takes the OSM data and compute a route with min user-cost according to the user's cost function. In OSMand you can sort of do this, because most of the OSM data is or can be on the phone. In Garmin, you can't, because we have to use the Garmin intermediate representation and because we have to use the Garmin routing engine. So, one could think about defining these user-cost functions, and then trying to have a transformation of OSM data to Garmin data such that the shortest time computation on the Garmin leads to a route that has minimal user-cost. > Do you suggest a new mkgmap option which overrides or influences the > results of the style? Can you give an example that shows the > advantage compared to a "private" style ? I think I'm really suggesting private styles, in some sense, but perhaps something more than that, which is a language to express these user cost functions and have that change the style. This is arguably way too complicated. Certainly it's premature until there is a style that does something that people find more useful than the default. What I was really trying to do was to express the notion that correctly encoding paved should not necessarily be the goal, but instead to allow most people to be able to create good routes. All that said, I find that around me, most connecting roads are paved and it doesn't matter much. In Upstate NY, there are connecting roads that are unpaved. But there, you really want to ask the question "would I rather drive 10 miles unpaved or 50 miles paved" rather than just "avoid". This reminds me that max_speed isn't really the right thing either, but OSM doesn't yet have a culture of "typical_speed". To me, routing is all about "on this route, what will my total experience be, and will I prefer it to this other route's experience". And that's very hard. So thanks for listening, and hope it was worth your time!
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