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Cave Surveying Discussion

This topic contains 8 replies, has 2 voices, and was last updated by  Peter Freeman 5 years, 3 months ago.

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  • #557

    Peter Freeman
    Moderator

    I use Fountainware’s ‘Cave Compass’ software for data reduction and plotting of my cave surveys. Compass can interpret LRUD data as relating to the TO station or the FROM station of a survey shot. Of course you must tell the software (in ‘settings’) which way to use the data. I think the default is FROM.

    I tend to measure my LRUDs at the TO station. This means that in dead-ends I don’t have to create a dummy (zero-length) shot in order to get LRUDs at the passage-end. The downside is that I have no LRUDs at the start of a survey leg, especially, for example, at an entrance. If necessary, I create a dummy shot there.

    My reasoning is that a typical cave has many more dead-ends than entrances (or other survey start point), and so I use the TO-station method.

    Any thoughts? I’d like to hear the views of experienced surveyors.

    #1530

    Peter Freeman
    Moderator

    For in-cave surveying I use a Leica Disto D3 to measure distance and inclination, and a Sunto KB14 compass for azimuth. There have been, for some time now, certain ‘home-brew’ options to measure all three required dimensions using [i:6xauqkzh][b:6xauqkzh]just one[/b:6xauqkzh][/i:6xauqkzh] instrument: The Shetland Attack Pony (SAP) from UK is one, and it also automates the transfer of data to a Palm Pilot PDA so there is no need to take a notebook into the cave except for sketching; The ‘Disto X’ is a third-party add-in daughter board for a certain Leica Disto model (A5 I think), which does much the same. Being ‘home-brew’ solutions, these devices suffer from the usual problems of dodgy firmware, lack of technical support, unreliability, etc. Also, I understand that calibration is a pain, and required rather too often.

    There [i:6xauqkzh][b:6xauqkzh]are[/b:6xauqkzh][/i:6xauqkzh] commercial units that seem to fit our requirements, though they are expensive. My reservation, apart from the expense, is whether they are rugged enough for the cave environment.

    The TruPulse unit is here:

    http://www.precisionlasers.com.au/image … lse360.pdf

    The Laser Ace unit is here:

    http://www.mdl.co.uk/resources/LaserAce … _06_06.pdf

    The Laser Ace is perhaps the right choice for us: better accuracy at our usual shot lengths.

    If you have 2.5 to 3.0 k$ to spare, I think these would be really good gadgets to try out.

    Comments sought!

    (Thanks to Neil for first sending me the TruPulse links)

    #1531

    Peter Freeman
    Moderator

    I asked Bob Kershaw for his view on the LRUDs issue. Bob is very experienced in this area as he manages the survey data and mapping for the Bullita system, Australia’s longest cave. Here is his reply:

    "Hi Peter. The short answer is what ever suits you. Providing your survey party knows what you are doing and, if you have someone else input the data, [that they know what you are doing]. At Bullita the LRUDs are made at the FROM station: a historical protocol and one which I think most people do in Australia. I appreciate the dead end bit comment – worthwhile to think about. Cheers, Bob"

    #1532

    Scott Hall
    Member

    It appears the LaserAce inclinometer only has a range of -70° to + 70°. I believe that may rule it out as a candidate for cave surveying.

    #1533

    Peter Freeman
    Moderator

    Scott, that’s a good observation – I hadn’t noticed that part of the specification. However, in practise it would not be a great problem and certainly doesn’t render the unit unsuitable.

    My Leica disto D3 only measures up to +-50 degrees inclination. However, while verticals (90 deg) are quite common, I hardly ever find myself measuring very steep slopes (which surprises me, but it is so).

    On those rare occasions I simply estimate: I interpolate between 50 degrees, which I can reach on the instrument, and vertical, which I can judge quite well. The method is to point the laser spot up (or down) at the max (50 deg), then pass through the target point and get to a vertical position of the disto, and then estimate how far the target pass-through was along that tilting motion. Sounds complicated, but actually easy to do.

    #1534

    Peter Freeman
    Moderator

    Comments on the Leica Disto D3, now that I have 2 years experience of using it heavily:

    1. Functionality is good, as expected.

    2. Battery life can be a problem – certainly turn it off between every shot, and don’t keep the laser running longer than necessary.

    3. The ‘maximum-distance’ function, potentially excellent for those shots to inaccessible narrow tube far-ends, needs care. It works, but occasionally will give readings way too high. I think this is a reflections issue – the incorrect readings may be double and triple the real distance. The solution is to apply reality checks, and repeat the measurement as necessary.

    4. I am on a warranty-replacement unit – my first one gradually developed a problem where the clear/off button did not work. Warranty was ‘no-questions-asked’ – nice.

    5. I am currently experiencing another problem: sometimes the laser does not turn on! A good clout always fixes it, so perhaps a bad connection? It’s not the battery connection, as the unit is otherwise fully powered up and functional. I suppose this problem, and above in (4), may be related to the harsh environment in-cave.

    6. A great design improvement would be for the ON button to require a long press, as does the OFF button, since it frequently gets turned on accidentally in a pocket: VERY annoying!. Most of the time I carry it in a pelican case with my compass and target-lamp.

    7. I wish it used AA rather than AAA batteries.

    Summary: Overall, an excellent purchase.

    #1535

    Scott Hall
    Member

    Nikon makes a waterproof model but it appears to be lacking a compass.
    [url:3suusdef]https://www.prospectors.com.au/p-8627-nikon-forestry-550.aspx[/url:3suusdef]

    Leica also have a new model, the D8.
    [url:3suusdef]http://www.leica-geosystems.com/en/Laser-Distancemeter-Leica-DISTO-D8_78069.htm[/url:3suusdef]

    #1536

    Scott Hall
    Member

    I found an IP67 (dust and waterproof), drop 1m to concrete, GPS, Compass w/tilt 90 degrees, 5MP camera, laser rangefinder.

    For redundancy, as they are only approx. US$5,000, they club should probably purchase two.

    http://www.junipersys.com/Juniper-Syste … ifications

    #1537

    Peter Freeman
    Moderator

    Back in November 2011, Seamus posed the question to me of whether compasses balanced for UK/Ireland would be satisfactory for use in PNG. My reply, which I have reasonable confidence of being valid, was as follows –

    Seamus

    I don’t have experience with using out-of-zone compasses, but here are my thoughts.

    1. Your comment "We were initially thinking that we could simply calculate any variations" is not applicable since the problem is difficulty-in-reading, not a systematic error.

    2. I imagine UK-balanced compasses (or Zone-5 Aus-balanced ones) will be radically different from PNG-balanced. The balance issue is related mainly to latitude: the angle with which magnetic lines of force intersect the earth’s surface varies with latitude, being zero on the (magnetic) equator. Since PNG is an equatorial location, its own compasses would require very little weighting, while those in the UK, being used quite far from the equator, would be significantly weighted. Not a good match!

    However, in your favour –

    3. Usage of compasses in caves is often quite different to usage on the earth’s surface (eg nautical, bushwalking). We cavers frequently have situations where we are not sighting horizontally: we are looking up or down to varying degrees, and these situations produce the problem of ‘sticking-card’. We get around it by being smart – tilt the compass up-and-down to get the card to move, sight onto something above or below the real target, etc. This problem is much the same as using an out-of-zone compass in a flat environment, where the issue is also ‘sticking-card’. In certain in-cave situations of looking up or down, an out-of-zone balance might actually be better! If it’s not, then back-sight that shot to make the out-of-balance issue go the other way.

    For this reason, I think you will probably get away with using UK compasses in PNG. But don’t count on it, or blame me!

    Regards
    Peter

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