[Tagging] Accuracy of survey

Kotya Karapetyan kotya.lists at gmail.com
Mon Dec 29 14:27:23 UTC 2014

Happy holidays and 2015 everyone!

> what is needed here is some tag, saying "don't touch these
> coordinates, they've been surveyed with high(est) accuracy".

I second this idea.

Just recently I discovered that something in this direction already exists:
Example: https://www.openstreetmap.org/edit#map=23/43.42272/6.76665
However it seems to be France-specific. I don't know if a similar thing
exists e.g. for Germany.

Since such reference points are quite common, I would support the idea of
creating a special tag for them, requiring that they are not moved. However
we need a clear consensus on how we define the "sufficient" accuracy and
how the data for such points will be updated.

I disagree with the point of view that an accuracy sufficient for consumer
GPS devices is sufficient for OSM and therefore there is no problem here.
Nobody ever declared that OSM is for smartphone users. We are trying to map
the world, and accuracy should be of primary interest for this project.


On Thu, Dec 25, 2014 at 7:16 PM, Rainer F├╝genstein <rfu at oudeis.org> wrote:

> TP> It was not clear if the OP indeed wants to map pipelines,
> TP> or was just quoting the pipeline expert for his opinion about
> TP> surveying methods.
> the latter. I'm referring to all nodes, not just pipelines & marker.
> Just used the conversation I had some time ago as an example.
> W> Terms !!
> W> In Metrology (http://en.wikipedia.org/wiki/Metrology) the words
> W> accuracy, error, etc have specific meaning ..
> please forgive my ignorance - let the experts decide on a proper term
> to be eventually used as tag. "dilution" comes to mind, but that's GPS
> specific, if I'm not mistaken.
> FV> Even if you collect plenty of GPS traces with no systematic error,
> these
> FV> still cannot beat a theodolite triangulation.
> when specifying "accuracy", the source of the coordinates shouldn't
> matter. It could be GPS, DGPS, theodolite triangulation, a file
> provided by officials or companies ...
> FV> I used estimated_accuracy=* or gps_accuracy=* a couple of times,
> IMHO, that's the way to go. would recommend against gps_*, see above.
> also, there should be a distinction between estimated and actual
> accuracy.
> FV> but I doubt
> FV> that it prevents other mappers from moving or even deleting them. Some
> use
> FV> editors like Potlatch, so they are not aware of tags. Some do
> thousands of
> FV> edits, all of which are validator based "corrections". They do not ask
> nor
> FV> think nor look at tags, except at those reported by the validator.
> software evolves; if such a tag is considered useful and widely used,
> it may eventually be supported by the developers. of course, there'll
> always be the black sheep ...
> FV> Also, there is no clear line between high and low precision data.
> Should an
> FV> editor warn when the precision is better than 1m, but ignore a
> precision of
> FV> 2m? This all depends on the precision of the new data, which the
> editor does
> FV> not know.
> for starters, I'd begin with a general warning if the precision of the
> existing node is less or equal than 2m (thats better than what the
> average consumer receiver can achieve). to draw a line between high
> and low precision, this article [1] may be helpful.
> some GPS receivers show the current precision in meters; GPX files
> contain HDOP/VDOP/PDOP if provided by the receiver. In theory and if
> provided, when a GPX file is used as source for nodes, precision could
> be derived from this information (by whatever means).
> FV> There are no GPS traces for pipeline markes.
> actually, there are ;-) I just didn't upload mine. but apart from
> that, pipeline mapping seems to be a few-(wo)men show, therefore it's
> more likely that pipeline operators may release their (high precision)
> data [2] before there are enough GPS traces to significantly increase
> precision via interpolation.
> cu
> [1] http://en.wikipedia.org/wiki/Global_Positioning_System
> (section "Augmentation" f.)
> [2]
> https://wiki.openstreetmap.org/wiki/Talk:Proposed_features/PipelineExtension#status_update.2F1
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> Tagging at openstreetmap.org
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