Laser measuring Vs. Pull tape

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Laser measuring Vs. Pull tape

Postby Lava tuber » Mar 9, 2006 12:30 pm

Does any one recommend laser light distance measuring devices, if so which ones? And how do they compare to just standard Survey pull Tapes?
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Postby Lava tuber » Mar 9, 2006 12:34 pm

sorry about the double post I thought you could not do that
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Postby Roppelcaver » Mar 9, 2006 12:57 pm

I do not have one, but we have used them in Roppel and they prove to be quite accurate, and good for wall and ceiling measurements.

The big downside is losing the tape as a frame of reference for a sketch. If you are trying to do really accurate sketches, the tape is invaluable for this. Without a tape, coupled with the propensity of a lasered shot to be long, the opportunity for distortions on your sketch can be enormous.

At least it is for me. Some, it seems, can do perfect work just by eyeball.

But, given the opportunity, having them for wall widths and ceiling heights, if nothing else would be great.

The tape is one of the most error prone parts of the survey (can't backsight a taped distance) and is the source of many blunders by good surveyors. I don't know how easy it is to screw up a laser shot, but that is a consideration in any event.
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Postby Cindy Heazlit » Mar 9, 2006 1:33 pm

I've been using laser gear for the last 2 years doing survey work in Hawaii and California Lava tubes. In my opinion, they are superior to tape - with some constraints:

Down side:
1) Don't work well in brightly lit environments, especially surface survey.
2) Can be dangerous and need proper working protocols (I've been hit in the eye twice now)
3) Heavier than tape
4) Not as rugged as tape - need some protection from the environment.
5) Need batteries
6) Many book people like to lay the tape down and walk it, placing exact locations of rocks etc. relative to tape.
7) Really expensive

Up side:
1) Can perform survey of passages "too tight" to go down. Do a forward sighting of compass, inclinometer and disto.
2) Significantly faster than tape
3) Tape gets hooked on the rough lava floor - lasers can't
4) Smaller than a tape on a reel
5) Can easily perform interim shots to significant features.
6) Ceiling shots are a breeze
7) Shooting through roots is a breeze (try laying a straight line through roots with a tape some time)
8) Very exact - reduce errors reading tape.
9) Nice for small tight passages. You don't have to squeeze to the wall to get a good reading.

As far as what is best - that is a matter of opinion. From all the distos that I've used, I would want:
1) Use AA batteries not special ones like AAA or 9 volt.
2) Some models have the switches really close together. You end up reprogramming the disto accidently, and all of a sudden your readings are in inches instead of feet. Get a good one that you can handle with your gloves on.

My favorite disto is the Leica A5, but I noticed that there is an A3 model that is significantly smaller (and slightly less accurate). Don't bother getting the ones with Bluetooth technology. A lot of money for functions you won't use.
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Postby hewhocaves » Mar 9, 2006 2:21 pm

Roppelcaver wrote:The big downside is losing the tape as a frame of reference for a sketch. If you are trying to do really accurate sketches, the tape is invaluable for this. Without a tape, coupled with the propensity of a lasered shot to be long, the opportunity for distortions on your sketch can be enormous.

At least it is for me. Some, it seems, can do perfect work just by eyeball.


i can do the eyeball sketch comfortably so long as the shot is under 25'. after that, i usually ask for someone to tell me where the middle is, and then place a pack or something there so i can break it up.

I also keep all my shots at 50' or less. 100' shots are really annoying to sketch. And, quite frankly, I haven't found borehole so boring that there's nothing to sketch.

I would be more worried about the shot itself being long. over hundreds of stations that can cause some serious error.

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Postby ian mckenzie » Mar 9, 2006 2:46 pm

Cindy Heazlit wrote:Can perform survey of passages "too tight" to go down.
I've always thought that passages too tight to enter should not contribute to a cave's surveyed length, and have never included them on one.
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Postby hewhocaves » Mar 9, 2006 3:17 pm

ian mckenzie wrote:
Cindy Heazlit wrote:Can perform survey of passages "too tight" to go down.
I've always thought that passages too tight to enter should not contribute to a cave's surveyed length, and have never included them on one.


true... but mapping them can still contribute to the general knowledge about the cave.
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Postby Cindy Heazlit » Mar 9, 2006 4:04 pm

Roppelcaver wrote:snip... Without a tape, coupled with the propensity of a lasered shot to be long, the opportunity for distortions on your sketch can be enormous.


According to Leica:
The tolerance is not proportional to the measured distance, it is the same over the entire distance. However, over long distances, additional errors of +/-5 ppm (parts per million) (+/-0.5mm/100m) come into play.


Roppelcaver wrote:The tape is one of the most error prone parts of the survey (can't backsight a taped distance) and is the source of many blunders by good surveyors. I don't know how easy it is to screw up a laser shot, but that is a consideration in any event.


It is quiet easy to do a laser shot. So our answer is to take the shot twice. If both readings agree, then great! If not, we keep taking readings until we get them to agree (and they make sense). It appears to eliminate reading errors and targeting errors.

BTW, here is a brochure
http://www.nwbuildnet.com/stores/bm/tools/disto/pdf/Brochure_family.pdf

and a nice FAQ addressing measuring inaccuracies, techniques, etc.
http://www.leica-geosystems.com/cpd/en/products/laser_distancemeter/lgs_3943.htm
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Postby Cindy Heazlit » Mar 9, 2006 4:19 pm

ian mckenzie wrote:
Cindy Heazlit wrote:Can perform survey of passages "too tight" to go down.
I've always thought that passages too tight to enter should not contribute to a cave's surveyed length, and have never included them on one.


????

But now I can survey it with a laser. So if I can survey it, shouldn't I be able to include it in surveyed length? I can see down the passage, and see the features to sketch. If I need to know how far away something is, I take another laser reading.

What is the difference between going in to a cave to survey it Vs sending in the instrument? The cave is still the cave, and the passage is there whether I can go into it or not.
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Postby ian mckenzie » Mar 9, 2006 5:13 pm

I thought the UIS rules on cave length/depth were dependent on a human being able to go up/into/along it.
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Postby NZcaver » Mar 9, 2006 5:41 pm

ian mckenzie wrote:I thought the UIS rules on cave length/depth were dependent on a human being able to go up/into/along it.

Purely semantics.

We recently did a number of shots with my Disto of small sections of passage that we didn't crawl through (in lava tubes). This allowed us to get a couple of loop closures for side tubes linking back into the main passage. The reason we didn't crawl through them was not necessarily that someone wouldn't fit (given the right motivation), but more to prevent wear-and-tear on the cave formations/roots - and on the body! :wink:

If would have been difficult - if not impossible - to do the same shots with a tape. I agree with Cindy's excellent post giving the pros and cons of surveying by laser. But I have to say my Leica Disto Lite 4 (and a number of similar Distos I've worked with) actually do use AAAs, and not AAs. The battery life, in my opinion, is excellent (2 full weeks of use with the same set of NiMHs, and the battery indicator still showing full). Another factor to take into consideration is what type of target plate you use. I've heard complaints of how "bad" lasers are, which are often made by dummies who use someones hand as a target plate. I've found that about a 1-foot square piece of white spongy packing foam works great - and it folds up nicely to carry around.
I'm very happy with the couple of hundred bucks I spent on my Disto (used). I highly recommend trying one out! :banana:
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Postby Cindy Heazlit » Mar 9, 2006 7:29 pm

NZcaver wrote:But I have to say my Leica Disto Lite 4 (and a number of similar Distos I've worked with) actually do use AAAs, and not AAs. The battery life, in my opinion, is excellent (2 full weeks of use with the same set of NiMHs, and the battery indicator still showing full).


Well, I actually was looking at the probability of my having AA batteries on hand, Vs AAA or 9V. I always have AA on me for my lights. It is just more convenient to have all my equipment use the same type of battery.

NZcaver wrote:I've heard complaints of how "bad" lasers are, which are often made by dummies who use someones hand as a target plate. I've found that about a 1-foot square piece of white spongy packing foam works great - and it folds up nicely to carry around.


Yeah, I like the white packing foam too. A 1 ft square piece makes a big target, and the laser seems to work well off of it. Any it is very easy to jam into the pack!

My first comment after using a laser was... "I'm never going back!"
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Postby NZcaver » Mar 9, 2006 8:12 pm

Cindy Heazlit wrote:I always have AA on me for my lights. It is just more convenient to have all my equipment use the same type of battery.

Amen! But I'm not sure how many of the smaller Disto models (if any) do use AAs. I have a backup headlamp, a small camp headlamp, and a flashlight that all use AAAs anyway, so having a Disto that does is no big inconvenience for me. That white packing foam "target" (when folded) also makes a good pad to lean an elbow on if you're shooting azimuth/inclination on the floor.
Even with regular pads, some of that lava really bites! :eek:

Anyone have any comments about the new Stanley $100 laser that uses Leica optics? I haven't used one personally in-cave, but I've heard from 2 different users that it might be less-than-ideal for cave surveying. Another case of getting what you pay for, perhaps?
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Postby Roppelcaver » Mar 9, 2006 10:26 pm

My points were muddled...

The "distortion" I referred to is the one on the sketch that I get when trying to draw long shots without the frame of reference of a tape. My limited work with them shows that they are very accurate, although I don't understand how blunder prone they may be. But, as Cindy points out, you can shoot it twice.

My comment about taping errors was just about that. Traditional taping is the most common source of blunders. LDMs may help this variable.

We had to redo a survey in Roppel -- not because of the LDM, but because the shots were 300 feet long and the sketch was whacked as a result. There was no way to sketch well an elliptical tube with meanders with 300 foot shots.

Just shoot shorter shots, I guess.
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Postby Scott McCrea » Mar 10, 2006 8:00 am

We have been using a Disto for about 4 years and love it. It can certainly be done without but the "laser" (we call it the Allen Parson's Project) makes it a lot easier. The price is the biggest down side for me. However, Stanley now makes one that sells for about $100. Preliminary caver testing is good. Some WV cavers are using one. Maybe if Mark Passerby see this, he'll pass the info on here, hint. :waving:
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