Here are some ideas that are developing as I try out our DistoX and PocketTopo with Therion. (See and follow the relevant links) This page assumes you have some familiarity with DistoX, PocketTopo and the contents of the respective manuals.

As an alternative you might like to view the Cave Surveying Group Therion and DistoX Training Course Guide which has more complete instructions and sample data for you to practise with.

Disclaimer: I have no experience or qualifications in paperless cave surveying. I bought a DistoX, borrowed a PDA, and now I toss them into my cave bag and take them to the furtherest reaches of our current exploits. We are stumbling along with the process, and so far it's working out OK. These are some rules that I'm making up for myself to make sure it really does live up to the promise of being faster and easier than scratching on a piece of paper, even if we do pick up 10x more detail…

I welcome any insights you may have. Add them to this page.

For PocketTopo 1.22, 1.34-1.36 and Therion 5.3+

Some ideas to minimise confusion and data loss.

DistoX and Survey Sequence

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. Taking shots requires that the DIST button be pressed and released straight away. This is a silent process. Only after the distoX has determined the success or failure of the shot will a sound be made.
  • The above is almost impossible while wearing gloves and with the DistoX in a transparent drybag. The solution is to put a rubber band around the distoX over top of the DIST button, before you put it in a dry-bag, so you can locate the button by touch (or glue on top of DIST button a dress-button, piece of plastic, …).
  • It is normal way to use DistoX with diplay up. But if you'll use it with display on left side if the station is below DistoX, on right side if above, etc., you may use the target for DistoX.

DistoX with PDA

  • 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.
  • To separate each of the above groups of splay shots, you may like to take a short (+-0.2m) dummy reading, horizontal-ish to, say, your hand. This can provide the PDA person with a clear indicator within the data table that a new group has started. Recent enhancements in PocketTopo that help identify which survey data refers to which survey leg tend to make this unnecessary however.
  • Three (successful) shots to the same place means it's a survey leg, and the pda assumes you will now move to that place.

PDA Booking

ALWAYS when stop sketching switch PocketTopo to cave map view mode (middle icon) to avoid unwanted creating of accidental lines near borders of sketching area!

PocketTopo Key Points

The key points to note are;
1. Ensure all files that contain surveys that are connected to each other are in the same folder. PocketTopo will then display the centrelines of all these surveys in the background of the current survey and sketch. Do not keep any copies or other files in that folder.

2. Main reasons to start a new file are when a new days survey is started, a new survey is starting in a different location, or if the plan or elevation centrelines start overlapping (causing the sketching to become difficult). This way the centrelines of other surveys remain visible and only the sketches of the currently open file can be seen (reduces confusion). It also reduces the chance of accidentally changing the data from a previous days survey.

The definition of 'series' in the next two sections is quite restrictive, and in practice I ignore it, without I think, many consequences.

PocketTopo Station Numbering
  • The logic of PocketTopo numbering follows the so-called “Toporobot method”. You may find the description of this method here:
    • The cave survey is divided into a number of “series”, one or more for each survey trip. Each series has its own number beginning 1, 2, m… Each series starts with 0 and continues 1, 2, 3, … It means, the first station of first series has number 1.0, then 1.1, 1.2, 1.3 etc, the second series 2.0 and then 2.1, 2.2, 2.3, 2.4 and so on.
    • The station label m.0 is only used when starting at a previously unsurveyed location. If you are starting from an existing station, you use that stations name, then the next station is m.1, where m is the number of the next series.
    • Each series needs to be stored in it's own separate file. ie You use Menu.File.New when you need to start a new series.
PocketTopo Survey Loops and Connections

I break these rules (for numbering and series) regularly, and don't seem to suffer too many consequences. PocketTopo is getting better (1.36) but is perhaps helpful to know where it has come from.

  • The series MUST NOT cross itself. This means that loops can ONLY be formed at the start or end of a series. In PocketTopo you must divide surveys in a similar way, and start a new file for each series.
  • The series are linked at start or end points. That is, each series can ONLY attach to the start or end point of a different series, or to somewhere in the middle of itself. A series can also start or end without attaching to another series (but must be attached at one end if there are more than one series in the cave, unless of course you know the co-ordinates for a point in the 'disconnected' series).
  • This means that each survey station has one and only one number/name/label as far as PocketTopo is concerned (this can be relaxed once you get the data into Therion).

How to cross a survey 'series' How to join up all the survey 'series'

This is why series 4 (yellow) ends when it gets to station 1.4, and continues as series 5. Similarly for series 7 (green) to series 12, and series 8 (purple) to series 9.

PocketTopo on Trimble Recon

  • Our Recon PDA is set up so that the;

left soft button restores PocketTopo
right soft button restores File Explorer

  • Within PocketTopo, all files (series) stored in the same folder relate to the SAME CAVE. The folders MUST BE created in root of directory structure.
  • Note that the Recon (or PocketTopo?) often displays all recent files in the same window (UNLIKE typical desktop/laptop behaviour). So be careful.
  • Use PocketTopo.Options.Smart to automate station number increase after three consecutive similar shots.
  • Before you start surveying, use PocketTopo.File.NewCave then…
    • Make a note of <prefix> in the PocketTopo 'Actual trip' data. (As PocketTopo cannot use alpha prefixes or series names, it is much simplar to adopt a survey prefix that matches the series number)
    • First station for each trip set to 1.0, 2.0, 3.0 as appropriate (ie the series number or prefix)
    • Note Survey team members and roles
    • (If you edit this information after you have done some survey shots, it will not be associated with those shots already completed - you can manually over-ride this once you get the data into Therion however).
  • Make lots of comments for fixed points and survey legs in the data table, record the station the comment relates to as the comments are linked to legs, not stations!!
  • In data view if a station is selected, use the + - buttons to change the station number, rather than the keypad! It's much faster that way.
  • If drawings get cluttered due to passages running over top of each other, then PocketTopo.File.New locks in the previous data and hides the previous sketches so you can start afresh. If you want to edit the original file you can PocketTopo.File.Open later on (and you'll see all the other survey legs in black as well).
  • Back bearings are very easy, so it is possible to use inaccessible or magnetic stations within a traverse line provided there is a 'clean' accessible station each side of it. Only bug I have found so far with this is, when in Therion, the extended elevations are not plotted as one would expect, the extend direction gets changed inappropriately.

Now this next bit has been confusing the hell out of me. I don't think I've got it right yet, but anyway it might work something like this…

  • Branch (side passage) surveys; Select the station the branch starts from (in either the FROM or TO fields). Use ContextMenu.StartHere to start a branch. It inserts a blank row at the bottom of the table. You may need to tidy the numbering, and you must add a comment describing the new branch.
  • When the branch (side passage) is finished and you happen to want to continue the original passage survey that was interupted, select the last station of the original passage (I guess that must be in the TO field) then use ContextMenu.ContinueHere. It will insert a blank row at the bottom of the table, and after the blank row the numbering should continue from where the original passage left off. You should add a comment to the blank row.

Data Transfer from PocketTopo to Therion

You're going to need to make sure your PDA can talk to your big computer (and or use a memory card; see tip in next paragraph). Assuming a Trimble Recon and Windows XP, you'll need to download ActiveSync. If using Vista or Windows 7 then your computer will probably need internet access the first time you connect the PDA so it can download the files automatically.

PDA data storage tip: It is highly recommended to save PDA data directly onto a memory card rather than as well as internal memory of the PDA. This way, if your PDA was to get damaged/broken after entering a load of survey data then you can take out the card and copy the data off it. If the data is only saved onto the internal memory of the PDA then it will be lost if the PDA is not longer working. If your data file is on the memory card then you can just put this in a computer and do not need to get the PDA to talk to the computer at all. Footleg:June 2013

Modifying Footleg's advice a little… To maximise chances of recovering data, save your working files to the PDA internal memory (PocketTopo then automatically keeps a pair of running backups on a memory card (if present)). If you create a new survey while in the cave, make sure you copy your previous survey file to the memory card, as PocketTopo continuously overwrites it's backup pair. Bruce:Dec2014

This next bit generally encapsulates getting to step 4 'insert background images' of my drawing checklist when you are 'paperless surveying', and includes examples that follow my own evolving naming convention. You can use your own names…

  • Remember to tidy up any data table comments and drawings before transferring data from the pda (Older PocketTopo versions only allow drawing modifications when used on a touch-screen device).
    • Cross sections: Stations and splay legs visible in PocketTopo sections are not transferred to Therion (Older PocketTopo versions only), so I work around this by sketching over them and clearly labelling them, so that they will be visible in the Xtherion drawing editor.
  • Open PocketTopo & Export filenames as follows;
    • PocketTopo.File.Save: <Prefix>-<PassageName>.top (native pocketTopo file)
    • PocketTopo.Export.Text: <Prefix>-<PassageName>Text.txt (not necessarily required, but more human readable than *.top or *Therion.txt files. Is ONLY way to read station and leg comments without using pocketTopo software)
    • PocketTopo.Export.Therion: <Prefix>-<PassageName>Therion.txt (transition to Therion file)
  • Now get these files into Therion;

(As an alternative to the description below, you can generate .th and .th2 files directly from PocketTopo .top files using TopParser by Andrew Atkinson. This inserts the leg and station comments for you. See Footleg:June,2013)

  • Therion[Editor Window].File.New: <Prefix>-<PassageName>.th (Therion survey data file)
    • File.Import: the *Therion.txt file you just created. It inserts all the survey data into the *.th file. You will need to add a survey data structure around this, and add any other meta data you would like included.
  • Therion[Map Window].File.New: <Prefix>-<PassageName>[Plan|ElevExt].th2 (Therion drawing data file -note that PocketTopo only produces extended elevations, NOT projected elevations).
    • In the 'Background Images' panel click the Insert button, select the same *Therion.txt (transition) file you just created. This creates an xvi file of the survey legs and sketches. See the sketch inserting and scaling tip below.
    • You can add multiple xvi files, or multiple copies of the same xvi file to a single .th2 file. The trick to doing this is to untick the visibility property for all of the existing background images before inserting a new one.
    • The other trick is that they all insert at the same location within the Map Window (seems to have been fixed in 5.3.9). It seems that to successfully move an xvi image you need to untick the visibilty property for all the other images, then in the usual way, double right click and drag to move the image. You may need to click the Auto Adjust Button in the Drawing Area tab to be able to access all of the drawings.
  • If you have used an alpha survey prefix, add it to each survey centerline with station-names <prefix> [] in the *.th file (not needed if you adopt the pockettopo series number as the prefix).

This saves a lot of typing. See Drawing Checklist > Scrap eg

    station-names AA[]

You can change the prefix or suffix (or both) sequentially by inserting new station-names statements throughout the file.

Scraps drawn over the xvi files will automatically record the 'PocketTopo' name of survey stations when they are drawn. Get Therion to add the prefix and suffix (@SurveyName) to each station automatically by adding the following options to each SCRAP.

-station-names <prefix> @<SurveyName> -author <year> “<AuthorName>” -copyright <year> “NZSS”


  \ -station-names 23 @23-EntranceSeries -author 2009.11.20 "B Mutton" -copyright 2009 "NZSS"

This approach requires some modification when a scrap is comprised of stations with differing prefixes or suffixes. First, draw the stations in the scrap with the XTherion drawing editor, close and save the file, then open it with a text editor. Now you can add station-names statements sequentially with the revise statement. eg

  revise AA-EntrancePlan-s1 -station-names AA @AA-EntranceSeries 
  point 1063.22503937 587.2462992 station -name 9.4 #Therion will see this as AA9.4@AA-EntranceSeries
  revise AA-EntrancePlan-s1 -station-names JH @[] # [] to indicate no suffix
  point 1140.29503937 519.4162992 station -name 9.3@jh1 #Therion will see this as JH9.3@jh1

Now you can compile to test it works, then open the file with XTherion and continue drawing in the normal way.

Sketch inserting and scaling tip

If, in the Insert background image open dialog you cannot find your exported PocketTopo files, then in the 'files of type' box select 'PocketTopo Therion export (*.txt)

Now once you have selected the file and closed the dialog, Xtherion will ask you for the xvi properties. The defaults are; scale 1:200 resolution 200 dpi grid 1m

These seem to be fine for small cave passage, but for larger cave passages a scale of 1:500, 100 dpi seems to give a better zoom range in Xtherion. Also I have a habit of drawing my pencil sketches of projected elevations at 1:500. Sometimes I insert the extended elevation xvi and scanned pencil sketch into the same file. Matching scales and dpi values gives a better result.


  • Declination is not transferred from PocketTopo to Therion files. Update *.th file manually after transfer, else projected (not extended) elevations before and after assigning a co-ordinate system will differ in appearance, sometimes significantly.
  • PocketTopo stores the declination (and trip information like the date and the surveyors etc) that is set at the time a shot is received with that shot, and this association cannot be broken. If you subsequently change the declination (or other information), it only has effect for future shots. The declination is added to the compass bearing for the purpose of producing the sketch. So, if you enter an erroneous declination and take some shots, the drawing will be permanently skewed.
  • This effect can be used to advantage if you want to make sure the text in your 2D pdf maps will be aligned properly when the finished map is to be rotated. Enter a declination into PocketTopo that equals <declination> + <rotation>. The effect of this is to ensure that the xvi sketches produced will be oriented the same as the finished map, and so text -align variables will match the orientations of the finished map. The downside of this approach is that the coordinates of the stations stored in PocketTopo will be completely arbitrary. (So far I have not taken any notice of the coordinates in PocketTopo - if you accept this I don't think there are any other ramifications - but I might be wrong)

Troubleshooting Data Transfer

We've been (early to mid 2010) having trouble with frequent communications blackouts between our distoX and Trimble Recon pda (tentatively mostly resolved early 2011). The distoX usually indicates it has a blue-tooth connection (the icon flashes on and off) but the data transfer does not proceed. It can take some minutes before data transfer re-commences. The battery levels in both devices appear to be 'full'.

Here is what we have tried… compared with the degree of success…
Maintain the devices within 1m of each other and wait Somewhat successful, definitely better than if they are 5m apart
Gently thrust them towards and away from each other while humming a mantra As above
Avoid passages with dimension less than 1.5m, especially if the walls are wet Usually works
In PocketTopo toggle Connect/Disconnect/Auto Sometimes successful
Turn distoX off and shut down PocketTopo. Start PocketTopo and turn distoX on about 1 sec later Most successful?
In PocketTopo save the file Sometimes successful
Change distoX batteries well before you need to In combination with the above seems to be most successful, even though Beat assures me that this should not affect performance. We suspect that the frequency of spurious erroneous distance measurements increases when the batteries are getting low, particularly the last 1000 or so shots.

Tip: Well before your batteries die, pre calibrate a fresh set in a comfortable location during fine weather, mark the ends (see page 1 of ) and write the date of calibration on the batteries. Save the calibration file with the same date, and take the file and batteries with you from now on. When the batteries die in the middle of a survey, it's now a simple matter to change the batteries (if the cave is dry) and transfer the new calibration to the distoX.

We corrected a problem whereby the pda was not recognising the backup CF flash card because it was in the 'wrong' slot. Resolving this improved the above situation, but did not completely fix it.

Any further enlightenment will be gratefully received.

Here is Beat's suggested progression for restoring stalled communication. Keep moving down the list until the data transfers. Note that pocketTopo tries to connect at 5 sec intervals, so don't be too impatient. If your devices have been working happily together, then you almost certainly only need to try the first two options;

  1. Normally it suffices to switch off the Disto for a few seconds.
  2. The next step would be to restart (warm boot) the PDA.

If this does not help then we are heading towards a troubleshooting approach;

  1. Check the disto is not in 'silent mode' (A small 0 displayed at top centre of screen -Toggle this on and off by pressing AREA, AREA, REF, REF, CLR) Activating silent mode prevents any currently stored data from ever being transferred, so be careful. If you don't have the small 0 displayed, try this option last.
  2. Try to connect the Disto from the Bluetooth manager. The Bluetooth icon on the Disto should flash. This means the pda can 'see' the disto signal.
  3. Disconnect from the manager and try to connect from PocketTopo (Menu:Bluetooth:connect). If it fails check the Port setting in PocketTopo matches the port setting for the disto in the Bluetooth manager. If you have more than one disto, each one seems to need it's own unique port setting.
  4. If the connection works but no data is transferred, try to switch the Disto to calibration mode using the commands in the calibration menu. If calibration mode can be switched, this confirms data can be sent from the pda to the disto, and so the lack of communication in the other direction is indeed an anomaly. I had this situation with lots of data stored, and toggling silent mode on and off resolved it. Only took 6 weeks to figure it out :-? )

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 after changing batteries 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!


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 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.