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Some References

Cave Surveying Group Therion and DistoX Training Course Guide Comprehensive instructions and sample data for you to practise with.

Marco Corvi Effective DistoX with TopoDroid Improper use of the DistoX can lead to gross mistakes. This work reviews examples of bad usage of the DistoX and the functions provided by TopoDroid to avoid them.

DistoX usage in general

  • Remember that each button has at least two functions, one when it is pressed for a short time only, the other when it is pressed and held.
  • DistoX1: Taking shots requires that the DIST button be pressed and released straight away. This is a silent process. Only after the distoX1 has determined the success or failure of the shot will a sound be made.
  • DistoX2 will work as above, but it is better to press+hold the DIST button, as you are less likely to shake the device right when it is trying to stabilise the sensors for measurement.
  • The above is almost impossible while wearing gloves and with the DistoX in a case or transparent drybag. Solutions are; a self adhesive raised dot on the DIST button, or put a rubber band around the distoX over top of the DIST button, so you can locate the button by touch.

Survey Sequence

This next bit does depend on your preferred workflow, and on the settings, or 'Stations Policy' you have set in the sketching application you are using. It was originally written for PocketTopo, and is just one of a number of ways it could be done. It matches a TopoDroid survey data 'Stations Policy' setting of “Splays, forward legs”

  • When arriving at a station take all the splay shots (what used to be LRUD) BEFORE taking shots to the next station. Make sure the pda/person booking has recorded points and knows what they are after every 2 or 3 splay shots BEFORE taking any more shots.
  • When taking shots, imagine you are the pda operator trying to progress the drawing based on what you have already done. For large passages, chambers or wherever you are inspired to collect lots of detail, this might be something like;
  1. define cross section It it important to do it first, because all measured splay shots will define only the cross-section and nothing else. It prevent you from mess if too many splay shots was measured before. Ie for a quadrilateral section shape, this would be the four corners. For an arbitrary shape take maybe 8 shots around the passage section. (The 'to station' for these shots would be a - (a dash) for wall shapes and . (a dot) for “in cave” features (blocks, pits, chimneys, …) for in Therion)
  2. define passage plan shape generally along the line where the floor meets the wall generally in the direction the survey is proceeding. This could extend to picking up the ceiling if it is significantly different to the floor. (The 'to station' for these shots would be a - (a dash) in Therion – when implemented)
  3. define important plan features (edge of water, pits, speleothems, rigging or large rocks etc). (The 'to station' for these shots shots would be a . ( a dot) in Therion– when implemented)
  4. define passage extended elevation shape (long section) shape. Pick up general changes in floor and ceiling gradient or steps from the previous station towards the next station (unless already picked up). (The 'to station' for these shots would be a - (a dash) in Therion – when implemented)
  5. define important extended elevation features (ledges, pits, speleothems, rigging or large rocks etc). (The 'to station' for these shots shots would be a . ( a dot) in Therion– when implemented)
  • For smaller or relatively featureless passages the process can be simplified.
  • Three (successful) shots to the same place means it's a survey leg, and the pda assumes you will now move to that place.

Troubleshooting Erroneous Measurements

These are more warnings to be cautious and observant, rather that troubleshooting as such.

Battery Changes

ALWAYS carry out the accuracy test described here http://paperless.bheeb.ch/download/DistoXAccuracyPrecautions.pdf after changing batteries (or charging a DistoX2) and before the start of each days surveying. If you do have a small discrepancy in compass or clino and you are too lazy to recalibrate, you can always use the calibrate statement to compensate

calibrate compass 0.5 # half of largest difference in accuracy test
calibrate clino 0.2

Think carefully about the sign of the correction!

I have made a spreadsheet to help with this [TO DO post the spreadsheet]

Distance

We've noticed that spurious distance measurements are more common than we would like, maybe 2% of shots?? All of the ones we have noticed are more than the actual distance measured, usually by more than a factor of 2 or 3 (a typical case would be a distance of about 10m measured as either ~50m or ~80m for a sequence of 5 shots, with the latter two pointing at a completely different target - and in a passage where we could see no more than 15m), but there was one case in a wide open passage where ~15m was measured as 25m (and we are sure we were not missing the target).

This can manifest a little bit like the sticking of compass or clino (see below) except that the erroneous measurements are usually not identical - so leading you to believe it is a normal measurement discrepancy. One explanation is that the laser is bouncing off nearby walls. This is certainly sometimes the case, although I can only remember one instance where this was happening on a repeatable basis. Moving the target slightly can solve this issue.
I suspect this problem is more frequent when the batteries are getting low, down to their last 1000 or so shots (although Beat has assured me that this is unlikely). Note that the distoX battery indicator only deviates from 100% when there are perhaps 10 or 20 shots left (when you are using lithium batteries as recommended) so unfortunately it is not a useful indication of battery health.

Compass and Clino

Both the compass and clino sensors seem to stick sometimes. If you see that the last several compass or clino readings are identical regardless of the orientation of the distoX, then you can be sure they have 'stuck'. A very gentle tap with your finger usually fixes this (remember it is a delicate device).
Ferrous objects and (handheld) (electro-)magnetic fields will affect the compass of course. Take care not to use the distoX within say 300mm of your light, SRT gear, bolts etc.

  • distox.txt
  • Last modified: 10 months ago
  • by brucemutton