> On 5. Sep 2019, at 08:28, Olly Betts <o...@survex.com> 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
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