I am using OSM-Inspector quite a lot nowadays to check/correct not only my contributions to the OSM-DB but also to correct other peoples errors. It is a great tool. To me it has become apparent that there are many redundant/excessive nodes in many ways and if I see one I will eliminate it. It would be nice to have a JOSM-Plug-in the checks a marked way for these excessive nodes, highlights them, allow a de-highlighting, and a general delete of those nodes left highlighted.

asked 08 Oct '11, 15:08

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dcp
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closed 09 Oct '11, 07:37

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What are you defining as "excessive"?

(08 Oct '11, 15:37) Richard ♦

Have a look at relation=1369789 for an example. My guess that in this case up to 50% of the nodes are not required i.e. redundant.

If a way is straight and has three nodes then the middle node is redundant/excessive. It contributes nothing to the DB but does cost time to download each time it is viewed,etc.

I have no idea how many nodes could be eliminated but in the light of what is happening, see: http://www.openstreetmap.org/user/!i!/diary/15046 the reduction of redundant nodes should be considered with some priority.

(08 Oct '11, 15:51) dcp
1

Are you familiar with the built-in Tools/Simplify Way?

(08 Oct '11, 15:55) gnurk

no. is it a JOSM-plug-in?

(08 Oct '11, 16:00) dcp
1

I think Tools/Simplify Way is native. Don't you have it in your menu?

(08 Oct '11, 16:03) gnurk

I have a JOSM German version and it does have shift-Y tool and the translation would be "Simplify Way", so yes you are right and thank-you. Big Question: Does it work on areas and multipolygons?

(08 Oct '11, 16:14) dcp

There seems to be no problem to select multiple ways/areas and run Simplify Way, but as always you have to be careful and manually watch that Simplify Way doesn't remove details you don't want to be removed. Especially curved ways may suffer from this.

Another, potential, data loss may occur if a mapper has mapped a straight way and marked to-be-further-tracked-later-road-crossings as extra nodes on that way. But many times it's obvious that the extra nodes are just mapping noise.

(08 Oct '11, 16:41) gnurk

I have just tried the "Simplify Way" tool on a Multipolygon with 1977 nodes and it reduced the number to 1489 which is a saving of 488 nodes or about a 25% reduction. That is just great. But is it safe to use. Am I destroying something i.e. doing more harm than good for I cannot check those 488 nodes individually. And why is it not being widely applied. The reduction of redundant data should be a priority.

(08 Oct '11, 16:41) dcp
2

Personally I suspect the best answer is to tackle the problem at source: apply strict rules to imports (such as the Corine one you pointed to) and mercilessly revert those that fail to abide by them.

(08 Oct '11, 17:17) Richard ♦
showing 5 of 9 show 4 more comments

The question has been closed for the following reason "The question is answered, right answer was accepted" by dcp 09 Oct '11, 07:37


Not everything that OSM Inspector highlights is necessarily an error. There is no need to split ways (creating complicated relations), just because the way has more than 1900 nodes.

The number of nodes in a way has nothing to do with load on the tile server.

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answered 08 Oct '11, 16:45

Vclaw's gravatar image

Vclaw
9.2k893140
accept rate: 22%

Then I just don't understand the logic of the program. OSM-Inspector should only show errors. If it highlights valid data as well as errors why should I take the time to look at it. It becomes a puzzle and not a tool. Obviously I am not qualified to make judgement on the tile server load. I did not know that the sum of all nodes has no effect on the on the tile server load. Sorry!

(08 Oct '11, 17:27) dcp

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question asked: 08 Oct '11, 15:08

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last updated: 09 Oct '11, 07:37

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