Re: [Therion] Detecting errors
You could also indicate the misalignment with instrument correction commands, but i dont know the exact command at the moment. I think that would not with different orientations of the same device... > Am 05.09.2019 um 13:10 schrieb Max D : > > > >> On 5. Sep 2019, at 08:28, Olly Betts wrote: >> >>> On Fri, Aug 16, 2019 at 05:11:22AM +0200, MD wrote: >>> We also then to measure the same small loop at the beginning of each trip: >>> A-B in four device orientations >>> B-A in four device orientations >>> A-C in four device orientations >>> C-A in four device orientations >>> C-B once >>> >>> So I could calculate an SD based on that. >> >> You probably don't want to work out a set of SDs per-trip - > > Currently we set the SD per calibration - which works out to about every > second trip. We Take the "Error stddev" from Topodroid Calibration Results - > e.g.0.1058 in the attached Screenshot. > > Thinking of it, this might be the wrong approach because it only considers > the instrument. > >> *sd tape 0.002 metres ; 2 millimetres >> *sd compass clino 0.5 degrees >> *sd position 0.05 metres ; 5 centimetres > > Interesting. I will read up on the difference between tape and position > >>> For sone Devices errors seem to be bound very much to orientation. In >>> the data saved by TopoDroid you can see the device orientation and so >>> we could set a sd based on the direction in which the shot was taken. >>> I have nit investigated this further so far. Also because we have this >>> data only for about 20% of the cave. >> >> This is already taken into account - you tell Survex the SD for the >> "tape" (read laser range-finder), "compass" and "clino" (read magnetic >> field measuring devices) and position (how close to the station you >> actually measure from) and it uses the direction of the leg to produce >> a 3D set of expected errors, which are then summed along each traverse. > > But I would need a extra set SD data per device orientation. > So I know that if the display is to the right the Disto tends to reassure an > Azimuth 2 degrees to high and if the display is to the left. > And when the display is to the left it tends to give an Azimuth 1 degree to > low. > > But perhaps I just should try to do more and better calibrations instead of > fixing stuff afterwards. > > >>> TopoDroid also is able to flag an “magnetic anomaly” - i’m not totally >>> sure how but this als could be used in setting a per shot SD. i have >>> not looked much into this. >> >> I think you want to treat that as an in-cave indication that you should >> check for sources of magnetic interference and redo affected readings. > > Good Advice! > > Thanks! > > --max > > > ___ > Therion mailing list > Therion@speleo.sk > https://mailman.speleo.sk/listinfo/therion ___ Therion mailing list Therion@speleo.sk https://mailman.speleo.sk/listinfo/therion
Re: [Therion] Detecting errors
> On 5. Sep 2019, at 08:28, Olly Betts wrote: > >> On Fri, Aug 16, 2019 at 05:11:22AM +0200, MD wrote: >> We also then to measure the same small loop at the beginning of each trip: >> A-B in four device orientations >> B-A in four device orientations >> A-C in four device orientations >> C-A in four device orientations >> C-B once >> >> So I could calculate an SD based on that. > > You probably don't want to work out a set of SDs per-trip - Currently we set the SD per calibration - which works out to about every second trip. We Take the "Error stddev" from Topodroid Calibration Results - e.g.0.1058 in the attached Screenshot. Thinking of it, this might be the wrong approach because it only considers the instrument. > *sd tape 0.002 metres ; 2 millimetres > *sd compass clino 0.5 degrees > *sd position 0.05 metres ; 5 centimetres Interesting. I will read up on the difference between tape and position >> For sone Devices errors seem to be bound very much to orientation. In >> the data saved by TopoDroid you can see the device orientation and so >> we could set a sd based on the direction in which the shot was taken. >> I have nit investigated this further so far. Also because we have this >> data only for about 20% of the cave. > > This is already taken into account - you tell Survex the SD for the > "tape" (read laser range-finder), "compass" and "clino" (read magnetic > field measuring devices) and position (how close to the station you > actually measure from) and it uses the direction of the leg to produce > a 3D set of expected errors, which are then summed along each traverse. But I would need a extra set SD data per device orientation. So I know that if the display is to the right the Disto tends to reassure an Azimuth 2 degrees to high and if the display is to the left. And when the display is to the left it tends to give an Azimuth 1 degree to low. But perhaps I just should try to do more and better calibrations instead of fixing stuff afterwards. >> TopoDroid also is able to flag an “magnetic anomaly” - i’m not totally >> sure how but this als could be used in setting a per shot SD. i have >> not looked much into this. > > I think you want to treat that as an in-cave indication that you should > check for sources of magnetic interference and redo affected readings. Good Advice! Thanks! --max ___ Therion mailing list Therion@speleo.sk https://mailman.speleo.sk/listinfo/therion
Re: [Therion] Detecting errors
On Fri, Aug 16, 2019 at 05:11:22AM +0200, MD wrote: > We also then to measure the same small loop at the beginning of each trip: > A-B in four device orientations > B-A in four device orientations > A-C in four device orientations > C-A in four device orientations > C-B once > > So I could calculate an SD based on that. You probably don't want to work out a set of SDs per-trip - there would be quite a lot of random fluctuation in the observed SDs from such a short loop, and an equivalent instrument properly calibrated and used with suitable care really ought to be able to achieve similar SDs. Combining information from a lot of such small test loops would be interesting though. We've been doing some surface measurements at home with our disto-x2 while planning some building work and I did some experimenting with setting different SDs and looking at how the loop error values are, and I found the following SDs seem to be achievable with care: *sd tape 0.002 metres ; 2 millimetres *sd compass clino 0.5 degrees *sd position 0.05 metres ; 5 centimetres The tape/compass/clino are just taken from Beet's disto-x2 article: http://paperless.bheeb.ch/download/DistoX2.pdf I've glossed over exactly what a "precision" of 2mm means and assumed it's just the standard deviation. It might actually mean the SD is even smaller, but that's pretty much irrelevant as the compass, clino and position errors will swamp any contribution from the tape (1m at 0.5 degrees is 8.7mm). The position error reflects how close I think I can reliably position the spot I've marked on the back of the disto relative to the "from" station plus the error in where the laser beam hits compared to the "to" station. I haven't tested if those are still reasonable underground. There should be less electromagnetic noise underground, but it's often colder and wetter underground than in our front garden, and I've found misty or dusty air can cause problems for the disto. I'd be interested to hear what people can actually achieve in-cave. > For sone Devices errors seem to be bound very much to orientation. In > the data saved by TopoDroid you can see the device orientation and so > we could set a sd based on the direction in which the shot was taken. > I have nit investigated this further so far. Also because we have this > data only for about 20% of the cave. This is already taken into account - you tell Survex the SD for the "tape" (read laser range-finder), "compass" and "clino" (read magnetic field measuring devices) and position (how close to the station you actually measure from) and it uses the direction of the leg to produce a 3D set of expected errors, which are then summed along each traverse. > TopoDroid also is able to flag an “magnetic anomaly” - i’m not totally > sure how but this als could be used in setting a per shot SD. i have > not looked much into this. I think you want to treat that as an in-cave indication that you should check for sources of magnetic interference and redo affected readings. Cheers, Olly ___ Therion mailing list Therion@speleo.sk https://mailman.speleo.sk/listinfo/therion
