Can you please have a look at Bujumbura, Burundi, at Zoom 17? everything is filled with the orange colour of secondary roads, and only names and some icons are still visable. It is like every tile is flooded with the orange colour! what can be the error? in other zooms the problem is not there

asked 06 Sep '11, 10:36

Matana's gravatar image

Matana
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edited 06 Sep '11, 12:02

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banoffee
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Whilst I can't answer for the specifics of the rendering issue, I'd previously noticed a similar problem, where a very large area is "flooded" with graveyard at zoom level 14 in a remote part of Scotland (and again this disappears at other zoom levels)

See http://www.openstreetmap.org/?lat=55.9658&lon=-5.9907&zoom=14&layers=M

(06 Sep '11, 12:00) banoffee

According to #OSM, somebody had added a secondary road between 0,0 and somewhere in Bali. That's now been fixed. Tiles in Bujumbura now look OK when rerendered.

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answered 06 Sep '11, 14:43

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SomeoneElse ♦
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Great that this specific issue was tracked down and fixed, but for a more complete answer:

  • how does one track down similar problems (e.g. the graveyard mentioned above in scotland)? ... i.e. how was the Bujumbura one tracked down to the specific secondary road mentioned?
  • is there an identifiable software fault in Mapnik that needs correcting either to avoid a rendering problem from similar issues, or to allow the object causing the problem to be more easily identified by casual users?
(06 Sep '11, 14:59) banoffee

I can't help with the graveyard one, but re Bujumbura someone on the #OSM IRC channel happened to mention that there was more crud at 0,0 than usual (incuding a road starting there). Being nosy, I had a quick look at what it was before it got deleted. Most were "wheelmap" nodes but the secondary road was still visible in some tiles heading east, which brought to mind this question.

(06 Sep '11, 16:16) SomeoneElse ♦

The graveyard one seems to be fixed now too. Forcing re-rendering of the problem tiles earlier today still gave the dodgy graveyard. The only changeset that changed anything in the general vicinity was http://www.openstreetmap.org/browse/changeset/9228920 which doesn't appear to have changed anything remotely relevant to the problem.

The underlying rendering issue, and/or what normal mappers might need to do to locate the problem causing it and fix the data seems to remain a mystery, and presumably will have to wait until the problem recurs somewhere else for a proper investigation/fix.

(06 Sep '11, 17:44) banoffee

I can confirm this. It seems to be a rendering error. I checked the boundary of this problem

the south-western corner is this: http://www.openstreetmap.org/?mlat=-8.66794&mlon=25.20267&zoom=17&layers=M http://b.tile.openstreetmap.org/17/74712/68703.png

the south-eastern corner is: http://www.openstreetmap.org/?mlat=-8.66793&mlon=90.01891&zoom=17&layers=M

the north-eastern corner is: http://www.openstreetmap.org/?mlat=-0.02202&mlon=90.01101&zoom=17&layers=M

The problem exists only in Zoom17, as you can see the area is huge: 550 square degrees (covering half of the indian ocean as well). I doubt that this is a problem in your local area, instead seems to be something that went wrong in the rendering process. I already forwarded your problem to the Developers Mailing list.

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answered 06 Sep '11, 11:13

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dieterdreist
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edited 06 Sep '11, 14:26

well the only (but tedious) way to solve it I think is to look in JOSM for the graveyard in that Scotland area and to change it - hoping that a new rendering by Mapnik will solve the issue.

I will try that myself with Bujumbura, looking for secondary highways and experimenting with their tags as to see if a new rendering will solve the problem... wish me luck!

If someone has a better idea, PLEASE let me know!!!!!

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answered 06 Sep '11, 12:14

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Matana
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A better idea would be to get in touch with a mapnik developer (or advanced user who knows how to run their own tile server). Presumably there is some mechanism for stepping through the rendering code and/or running it in a "debug" mode to find out exactly what object is causing this rendering issue and why...

Edit: ... and probably the appropriate route to get in touch with them is to submit a ticket via http://trac.openstreetmap.org

(06 Sep '11, 13:11) banoffee
-1

thank you banoffee! I opened a new ticket, lets hope this critical error can be resolved!

(06 Sep '11, 14:16) Matana
3

It's not "critical" - critical would be if a whole country had turned orange at all zooms!

(06 Sep '11, 14:40) Richard ♦

After changing in JOSM the "Avenue Rusama" to a tertiary highway (for test purposes) the tiles in Zoom 17 were rendered correctly (right b4 that I checked and it was still wrong)! After changing it back to a secondary road the tiles are still rendered correctly. It seems the problem was with this one road in Bujumbura, though I have no clue as to WHAT was wrong. All I see is that it is now rendered well.

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answered 06 Sep '11, 14:50

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Matana
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2

It wasn't your road - it was another one someone added elsewhere that broke the renderer.

You can request a rerendering of an individual tile by right clicking the map, selecting "view image", and then adding "/dirty" to the end of the URL. It'll display "Tile submitted for rendering". The time taken for the actual rendering depends on how busy things are, but right now it's pretty quick.

(06 Sep '11, 14:54) SomeoneElse ♦
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question asked: 06 Sep '11, 10:36

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last updated: 06 Sep '11, 17:45

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