JOSM - How to show a road is over, rather than under another road

Buadhai · 2009-09-26T22:14:11.000Z

I don’t see any tool in JOSM that lets me indicate that one road is over rather than under another road.

For example, look here: Sam Yak Pak Junction

The trunk-link should be over, not under the unnamed road that is parallel to the railway line.

The roads are rendered properly by Osmarender and Cycle Map, but not by Mapnik.

What can I do about that?

Alex_McKee · 2009-09-27T06:29:17.000Z

If it’s over, is the trunk-link a bridge? Or perhaps the road goes under a tunnel?

Buadhai · 2009-09-27T07:06:04.000Z

^I don’t think that’s it. The trunk road itself is not tagged as a bridge, but it is properly shown as going over all the roads that it is really over. It’s only the trunk-link roads that are rendered improperly by Mapnik.

Alex_McKee · 2009-09-27T08:32:22.000Z

I’m not sure I understand. How can the trunk road go over the other road without some sort of bridge/tunnel? Or perhaps the entire road is on a viaduct?

Ldp · 2009-09-27T09:09:41.000Z

Mapnik still gets some ordering wrong. If you think your data is sound, don’t think too long about how mapnik shows it. It’s a complex issue (in mapnik), of stylesheet complexity, to stylesheet maintainability and even rendering speed.

Buadhai · 2009-09-27T09:39:23.000Z

Alex McKee:

I’m not sure I understand. How can the trunk road go over the other road without some sort of bridge/tunnel? Or perhaps the entire road is on a viaduct?

You’re right, it’s a massive overpass. But, none of the other nearby overpasses are tagged as bridges and they get rendered properly. It’s just this one that’s wrong.

I’m going to follow ldp’s advice…

Alex_McKee · 2009-09-27T09:46:49.000Z

If they’re overpasses they should be tagged as bridges. Just because there is an illusion of correctness in the rendering it does not make up for defects in the data. Any and all bridges should be tagged so properly.

OSM’s data structure is topological.

Buadhai · 2009-09-27T13:39:52.000Z

^Thanks for the reference. Just what I was looking for. I’ll see if I can fix this.

Alex_McKee · 2009-09-27T13:48:51.000Z

No problem, glad I could help. I usually dish out references where I can, give a man a fish and all that.

Buadhai · 2009-09-28T00:37:28.000Z

^Sometimes old men like me need a little extra push…

Ldp · 2009-09-28T07:06:29.000Z

Buadhai:

You’re right, it’s a massive overpass. But, none of the other nearby overpasses are tagged as bridges and they get rendered properly. It’s just this one that’s wrong.

I’m going to follow ldp’s advice…

Am I right in understanding that you think you don’t need bridge/tunnel tags, coupled with layer=*, when you see it’s already rendered ‘right’ on the map? That is a backwards assumption. The map should never be leading. If it’s one massive overpass, tag it as such, with appropriate bridge and layer tags.

That it currently shows up the way it does, in the absence of layer tags, is not an indication that it was tagged correctly. It just shows that the current drawing order in the stylesheet for mapnik makes it work out that way, but that may well change in the future, and you do need layer=* to indicate canonically which is the overpass and which way goes under that.

Buadhai · 2009-09-28T07:30:08.000Z

Ldp:

Buadhai:

You’re right, it’s a massive overpass. But, none of the other nearby overpasses are tagged as bridges and they get rendered properly. It’s just this one that’s wrong.

I’m going to follow ldp’s advice…

Am I right in understanding that you think you don’t need bridge/tunnel tags, coupled with layer=*, when you see it’s already rendered ‘right’ on the map?

No, you’re not right. Alex McKee persuaded me that if it’s not right it should be fixed. It’s just that I don’t yet have enough experience to do the job. It’s very complex. All of the highways leading into this interchange are currently shown as single carriageway. In fact they are all dual carriageway and all have frontage roads, only one of which is currently on the map, which I added.

Changing the highways to dual-carriageway and adding the frontage roads, which should be done first, will affect hundreds of kilometers of road and will require extensive editing of the roads which connect to the highways throughout those hundreds of kilometers.

At this point I don’t have the expertise required to do the job properly.

Someday, maybe; but not yet.