Getting the distance value from a highway milestone

[db4]

I need to work with highway milestones: https://wiki.openstreetmap.org/wiki/Tag:highway%3Dmilestone
Adding just

  TYPE highway_milestone
    = NODE ("highway"=="milestone")

to a stylesheet isn't going to work, distance tag value is not read to the feature value buffer. So I probably have to define Distance feature. How to do that? Can it be done in the stylesheet, or does it require defining the feature in the library itself?

[Karry]

Hi Dmitry. We do not have distance feature yet. You would need to define it in the code, see existing features. Then, you need to "register" it (in TypeConfig ?) and provide proper "label" to be usable in stylesheet...

I'm just curious, what is the purpose?

[db4]

Hi Lukáš, thanks for your answer. I'd like to resolve a location on a highway to the address like this: "Abc way, 27 km". DescribeLocation() did not provide this functionality, so I planned to do it manually: search for two closest highway milestones on the way and append the lowest one to the way description if found.

[Framstag]

Feature are a representation of tag data in the OSM database.

As far as I understand you, you want to dynamically calculate the distance between two point on the map. Correct?

In this case you have two options:

• Use the low level geo functions to calculate the direct distance ("direct line") between to geo coordinates
• Use the router to calculate the "navigatorial" distance between two nodes on the map. For this you have to look for the closest (connected!) node on the map for a geographical coordinate.

Since routing is rather expensive, most solutions return option 1 in case of a list of targets in the UI. Solution two makes sense for a single target but should be calculate async to the UI.

Does this help you?

You could of course also extend the Describe Location function with another strategy to solve the problem more generally. Though Describe Location should not call the router, since such cost would not be expected.

[db4]

Hi @Framstag

As far as I understand you, you want to dynamically calculate the distance between two point on the map. Correct?

Not exactly. I'd like to find the nearest highway milestone for the given road location, read distance value (https://wiki.openstreetmap.org/wiki/Tag:highway%3Dmilestone) and append it to the location description. Currently libosmscout doesn't allow to work with OSM highway milestones, as there is no feature distance. How to find the nearest milestone is another question.

[Framstag]

@db4 Thanks for your explanation!

The standard question for libosmscout (and possibly OSM in general) is. Are (in this case) nodes of type milestone or is milestone a optional feature for a node of another type ("is" vs "has")?

If I look at this example:

https://www.openstreetmap.org/node/898543#map=19/51.520207/7.679907

...it looks like in this case we have a "is" situation. @Karry, @db4 if you think different, please discuss!

In this case, ou should define a new node type "Milestone" which is defined by the references tag.

If this is the case, possible attributes of this type ("Features" in libosmscout speak) are "ref" (already existing) and "distance". Since distance is currently missing, this should be added as new feature and these features are assigned to the new type.

If you want to describe a location in relation to a location on a way, you would then load the way and scan the way (a defined distance) in both directions (up to to e.g. 5 km?), load way nodes and check if they are of type milestone. Possibly you also need to follow connected ways (if they are of the same type) if the way is not long enough for the maximum distance. Alternatively you load all ways of the given type in a given bounding box and resolve ways candidtaes afterwards.

Since the use case might have some interesting real-life use cases (car accident) it might make sense to implement this as part of the DescribeLocation feature as a new result variant.

I hope, this helps.

[db4]

I think we need a mliestone node. Something like this?

  TYPE highway_milestone
    = NODE ("highway"=="milestone")
    {Distance, Ref}

BTW, here is another example:
https://www.openstreetmap.org/node/2330448056
so one should use distance value if available, or parse ref text to get the actual distance

[Framstag]

Yes this would be the steps to implement.

Note however that your example is a bad example, since the milestone is not positioned in the highway. In this case it cannot be found by analyzing the highway and loading the nodes, but you would need a boundary search and have to match milestone and way based on closeness.

The English page mentions that positioning of the node is under discussion.