[Tagging] Clarification on the role link in route relations

[Dave F]

On 13/01/2022 21:41, Brian M. Sperlongano wrote:
>
>
> On Thu, Jan 13, 2022 at 4:21 PM Dave F <davefoxfac63 at btinternet.com> 
> wrote:
>
>     On 13/01/2022 18:30, Brian M. Sperlongano wrote:
>>     On Thu, Jan 13, 2022 at 1:16 PM Dave F via Tagging
>>     <tagging at openstreetmap.org> wrote:
>>
>>
>>         I'm intrigued by your Point 3.
>>         Please provide a link to it in OSM & details of your
>>         rendering (Github,
>>         website?).
>>
>>         DaveF
>>
>>
>>     The example is in the github link that Minh provided:
>>     https://github.com/ZeLonewolf/openstreetmap-americana/issues/79
>
>     Thanks for that, but it provides no info about this new rendering.
>     You mentioned Opentilemaps. Is that what they're using?
>
>
> This is getting deeper than the tagging list probably cares about, but 
> yes, this renderer is using an OpenMapTiles / mapLibre vector tile 
> stack, and the new version of OpenMapTiles that was released this 
> month adds support for concurrent road route relations.  The behavior 
> of OpenMapTiles with concurrent road route relations is that each way 
> contains a list of routes that the way is a member of (regardless of 
> role).  The front end renderer then takes that data and uses it to 
> draw one or more highway shields. The issue that prompted this 
> discussion was that in a few places, shields were appearing on ramps 
> TO a highway rather than just ON a highway.  This is because those 
> ramps TO the highway were added to the road route relation.
>
>>     I've just added a couple comments describing the possible
>>     technical solutions to this issue as well at the link one of the
>>     objects in question on the map, which I'll also paste here:
>>     https://www.openstreetmap.org/way/587338079
>
>     Cheers. That way is an 'exit from', not a 'link to' so it
>     shouldn't be a member of the VT 15 relation. The roads heading to
>     the V 15 should be included with link roles.
>
>
> You've contradicted yourself here.  First you say that way shouldn't 
> be a member of the relation, and then you say it "should be included 
> with link roles".  So it's not clear whether you favor including the 
> ramps (with link roles) or whether you favor not making them members 
> of the route relation.

Those roads are *oneway*. The one heading *away* from the route 
shouldn't be included because it's *not* a link *towards* the route 
relation.

>     However, this is a developer, not OSM database problem. They
>     should have filter rules to remove any data they're not interested
>     in.
>
>     Your Point 3 - When you say 'Remove relation |link| memberships
>     from the map' do you mean from their rendering or OSM database? If
>     the latter, I disagree.
>
>
> As a community renderer author, I feel that we have a special 
> responsibility to:
> 1. Render correctly when data is entered in correctly
> 2. Render incorrectly when data is entered in incorrectly
>
> Intentionally rendering bad data badly provides appropriate feedback 
> to the community resulting in better data for all users in the end.  I 
> would necessarily take a different approach on a commercial product, 
> where I would attempt to suppress mis-tagging rather than expose it.

It appears there's nothing wrong with the OSM database in this case, All 
that's required is a couple of lines on your code to filter the data you 
don't require.

DaveF
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