[Therion] Aven colour by loop error

[Stacho Mudrak]

​Hello,

it is already fixed in the latest release and therion is parsing survex
.err file for loop errors and outputs sigmas to .3d file. ​You may compare
data.3d generated by survex (in thTMPDIR when -d is used) and therion
generated .3d file, that they are equal when colored by error.

S.

On 3 April 2017 at 03:49, Olly Betts via Therion <therion at speleo.sk> wrote:

> On Sat, Apr 01, 2017 at 09:10:02PM +1300, Bruce Mutton via Therion wrote:
> > The new capability of exporting loop closure information to 3d format is
> > helping to identify the bad loops on our surveys.
> >
> > Very nice.
> >
> > However the scalebar at the top right seems to be locked into a range of
> 0.0
> > to 12.0 (%) error.
>
> Aven's error scale isn't in %, but rather in "sigmas" - i.e. it's how many
> times the expected error the observed error is.  Assuming normal
> distribution
> of errors (which sums of random errors will tend towards) anything more
> than
> 3 is only 0.3% likely by random errors, so highly suspect:
>
> https://en.wikipedia.org/wiki/68%E2%80%9395%E2%80%9399.7_rule
>
> If what Stacho said back in February is still true, therion outputs the
> wrong data in this field in the 3d file, so you actually see "2 * relative
> error of a loop" there, by which I think he means percentage misclosure.
>
> But as I said at the time, percentage misclosure isn't really a useful
> measure of loop quality because the threshold of what is reasonable
> varies with the length of the loop:
>
> https://mailman.speleo.sk/pipermail/therion/2017-February/006300.html
>
> > This is OK for our really nasty loop closures; the maps look suitably
> > colourful, but some of our more recent cave surveys don't have error much
> > more than 1.5%, so the picture is kind of shades of blue, as below.  It
> > doesn't help with visualising the relative quality of the loops.
>
> Unless Stacho has since fixed this, you're actually seeing 0-6% there
> currently.
>
> > Would it be possible to change the default scalebar to something like
> 0.0 to
> > 2.0, with the upper limit stepping upwards to suit the data, if there are
> > larger loop errors?
>
> I'd much rather we fixed therion to export the correct error information.
> Trying to colour based on percentage error just seems to be fundamentally
> a less helpful approach.
>
> Also, not varying the colours for a particular number of sigmas depending
> on
> how bad the data is was a deliberate choice.  2 sigmas is no better or
> worse
> just because someone blundered a survey elsewhere.  And if data is
> surveyed to
> a lower quality the grades should be set appropriately to reflect that.
>
> Cheers,
>     Olly
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