I see that the average speeds are essentially hard coded based on road types, is this then what is used in calculation of ETAs and working out the best route?
If I have data on the true average driving speed or want to use some function of the road speed limit is there any way to force it to do this?
A final question if you know, if I do have the correct average driving speeds would there be a way to force the engine to use these speeds when calculating the best route?
My current thought process is the following, do you think I am on the right track?
Create a custom TagParser for my new tag say true_driving_speed
Override DefaultImportRegistry and add an entry in the createImportUnit function for my new tag.
Where I am unsure is how to force the routing engine to use my speed as the road speed, Is the default speed value used by the routing engine max_speed, because if it is I can assume (I think) true_driving_speed will be lower than max_speed so I can create a custom model with
If you are using a recent GraphHopper version you will see that the car_average_speed is used explicitly in the custom model (see config-example.yml, which points to car.json which uses car_average_speed). You could simply use 'true_driving_speed` there instead (without relying on true_driving_speed being lower than max_speed or something). You could also modify CarAverageSpeedParser to plug in your own speeds there.
Thank you for the response, when I look in the car.json though it uses the limit_to function for the car_average_speed, my understanding of the limit_to is it would take the minimum of the road speed and the car_average_speed thus if the road speed was lower than the car_average_speed for whatever reason this would resolve to the road speed.
i.e. its also relies on the fact that the car_average_speed is lower than the road speed.
My thoughts are is there a way to explicitly set the speed value on the road, i.e. override the road speed wth the true_driving_speed rather than just limiting it.
Yes, limit_to only limits the speed, but the default speed is unlimited. The default speed used to be car_average_speed implicitly, but in recent GraphHopper versions it is unlimited, which is why there is now this explicit rule limiting to car_average_speed. If you remove the limit_to: car_average_speed rule you should get an error saying that you have to limit the speed. So basically the first limit_to rule sets the speed.
Yes. if: true, limit_to: true_driving_speed (as first statement in the custom model) will set the speed to this exact value, just like if: true, limit_to: car_average_speed sets it to car_average_speed.
