[Tagging] Node objects in tunnels or on bridges?

[Richard]

On Mon, Jun 08, 2015 at 07:10:08PM +0200, André Pirard wrote:
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>     On 2015-06-08 13:29, Richard wrote :
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>       Hi,
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> quite often there are node-type objects on bridges or in tunnels.
> 
> What to do with them? Tunnel or bridge tags are dfined only for
> ways.
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>     In my mind:
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>       bridges are piece of concrete below the roads (tarmac) and
>         hence should be tagged at level=-1
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>         they should not split the road but be overlaid as in
>           the real world, rendered with two stripes extending on both
>           sides of the road, look at an aerial photo of a bridge; but it
>           wouldn't hurt if the renderer decided to make it artificially
>           more apparent
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>         
>         they may have their own attributes, like a name, without
>           overwriting those of the road

There is man_made=bridge for this purpose. For the time being the ways 
running across the bridge still need to be split and marked with layer & bridge
but hopefully this requirement will go away sometime in the future:
 http://wiki.openstreetmap.org/wiki/Proposed_features/Simplify_man_made%3Dbridge_mapping

For small bridges represented by a single line however, "overlaying" the
bridge over the road would cause more complications than it would solve.

BTW I hope you don't tag all bridges with level=-1 in real world mapping???


>       streams and rivers repeatedly pass under bridges and culverts
>         and there is no good reason to have them step up and down on
>         each occasion
>       
>         they should be tagged at level=-2 full length

we have had this discussion before. Change of layer does not mean
change of elevation in real world. 
For technical reasons it is not desirable to tag overtly long objects 
with layer: if the object extends beyond your editing area/the data you 
have downloaded there is no way your tools could verify whether it 
creates a layer conflict somehwere far outside your editing area. 
Since there are other objects in the database assigned with layer=-2 
you wil sooner or later create such conflicts.

>         culverts should be tagged at level=-1

so in your view the waterway would step up to flow through the culvert?

 
>     And the consequences regarding what you ask is that the objects,
>     like waste bins, are not necessarily on the bridge or in the tunnel
>     but can simply be on the road.  Isn't that getting logical?  

yes, that is logical. It would require adding the information whether it is
right or left from the center of the road and renderers and other tools
learning how to cope with it.

Does it work in practice?

>     ....                                                        But it
>     would be possible to hang them on tunnel walls as tunnels shouldn't
>     be ways but different objects (as another logical consequence).

man_made=tunnel in analogy to man_made=bridge anyone? There is also 
  http://wiki.openstreetmap.org/wiki/Relations/Proposed/Bridges_and_Tunnels
 
which may be unnecessary complicated for many purposes.

>     Avoiding splits, especially for streams and rivers, is a help for
>     Nominatim to not show tiny pieces of ways (1).

unfortunately there are milions of reasons other than bridges/tunnels why 
people split ways. Presumably all the parts of the ways could be collected
in relations which is mostly done with waterway relations but for other ways
most people think that the tools (like nominatim) should cope with way 
fragments as they are now.

>     (1) and the final step towards avoiding splits would be my OVERLAY
>     aka SEGMENT proposition, but there's never been a reply to this
>     message.

haven't noticed this proposal.

Richard