[Tagging] Accuracy of survey
rfu at oudeis.org
Thu Dec 25 18:16:04 UTC 2014
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
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  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  before there are enough GPS traces to significantly increase
precision via interpolation.
(section "Augmentation" f.)
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