footleg
New member
Having just spent a week surveying with a laser measure for the first time, I can provide some first hand feedback.
Firstly, it is far, far quicker than surveying with a tape. Especially for Left,Right,Up,Down readings and when only 2 people are doing the surveying. Allows the sketcher to keep their hands clean for drawing too.
Secondly, it is difficult to hold the spot steady on long (20m+ legs). But if you choose your target carefully so there is not anything next to it where the distance will be very different (e.g. choose a flat wall or stand in front of it and use your body as a target) then this can be overcome. Double check long readings to be sure. We rarely get legs over 10m anyway in my personal experience.
Thirdly, the laser is a great help in choosing stations, as it instantly indicates which points along the passage are visible from the last station when the user shines it around from the last station.
Finally one drawback we had not anticipated. One of our team was red/green colour blind, and could not actually see the spot of the red laser on mud and rock!
Overall I was completely sold on them. We worked as a pair, me drawing and recording the figures, and my survey partner reading the instruments. I set stations and used my hand as a target, so no problems with reflections off difficult surfaces. Surveying in wet cold conditions was fast and efficient. We could also measure the heights of avens. Got a reading of 35m up one, so reflections off rock are possible over long distances.
Firstly, it is far, far quicker than surveying with a tape. Especially for Left,Right,Up,Down readings and when only 2 people are doing the surveying. Allows the sketcher to keep their hands clean for drawing too.
Secondly, it is difficult to hold the spot steady on long (20m+ legs). But if you choose your target carefully so there is not anything next to it where the distance will be very different (e.g. choose a flat wall or stand in front of it and use your body as a target) then this can be overcome. Double check long readings to be sure. We rarely get legs over 10m anyway in my personal experience.
Thirdly, the laser is a great help in choosing stations, as it instantly indicates which points along the passage are visible from the last station when the user shines it around from the last station.
Finally one drawback we had not anticipated. One of our team was red/green colour blind, and could not actually see the spot of the red laser on mud and rock!
Overall I was completely sold on them. We worked as a pair, me drawing and recording the figures, and my survey partner reading the instruments. I set stations and used my hand as a target, so no problems with reflections off difficult surfaces. Surveying in wet cold conditions was fast and efficient. We could also measure the heights of avens. Got a reading of 35m up one, so reflections off rock are possible over long distances.
Cave_Troll
Active member
anfieldman said:A tape can bend causing inaccuracies. Laser light as we know does not bend.
Actually light can and does bend.
However the effect is not likely to be noticable by you down a cave unless there is a small Neutron Star in the next chamber.
Christian_Chourot
New member
Cave_Troll said:anfieldman said:A tape can bend causing inaccuracies. Laser light as we know does not bend.
Actually light can and does bend.
However the effect is not likely to be noticable by you down a cave unless there is a small Neutron Star in the next chamber.
Or an average-sized caver.
footleg
New member
graham said:
Body as target is just for measuring distance to station. The laser is still aimed for my hand held flat against the body, but prevents misreading is the laser wobbles off the hand area. Compass and Clino are then sighted onto a finger held first vertically for compass, then horizontally for clino. Instrument reader then comes up the the station and reads from the same point as the finger was held (i.e. one body width out from the wall adjacent to whatever prominent feature I picked to stand in front of for the station. It is quite practical to get positional accuracy within the 10cm allowed for station positioning for grade 5 surveying.
Cookie
New member
footleg said:
When surveying our finds in Torno we used the survey notepad as the target for the reasons you give. Good signal reflection and easy to sight on since a clear target at a distance. On the longer legs a steady hand is required, not so easy after a late night session in Bar German
, but managed 20m legs OK.
menacer
Active member
I had the steadiest hand in the group so got the job of surveying the 35m legs in the new cave in Matienzo (thanks to the pringle'dingle team) If you have a steady hand 35m is no problem. We did turn the brightness up on the pony afterwards though as battery power wasnt a problem but seeing the dot was.......the disto spot was excellent.... :tease:
Robert Scott
Member
Have you considered using a "lolly" as in this Avalon item
http://www.scavalon.be/avalonuk/technical/laserclino.htm ?
http://www.scavalon.be/avalonuk/technical/laserclino.htm ?
Ouan
Member
Hi
Had a test drive of a SAP, used with with a Disto, last week in a 325m long cave in Thailand.
Came to the same conclusions as most of the folks above: my geriatric companion had problems holding the SAP and Disto steady enough for readings over 20m (longest leg achieved 26m); sighted onto survey book; for two old, blind buggers with glasses the SAP is better than Suuntos in hot and steamy conditions; SAP gives you get two readings at once and you know where you are pointing it, plus electronic back up of data; SAP and Disto are lighter and more compact that Suuntos and tape.
Our accuracy wasn't brilliant: one 100m loop had a 6% closure error and a 92m loop had a 3% closure error. According to Walls the errors are mainly in the distances, so next time we'll take the distances twice to make sure the Disto is actually measuring to the target and not bouncing off the wall behind. However, the survey was good enough for our purposes.
Ouan
Had a test drive of a SAP, used with with a Disto, last week in a 325m long cave in Thailand.
Came to the same conclusions as most of the folks above: my geriatric companion had problems holding the SAP and Disto steady enough for readings over 20m (longest leg achieved 26m); sighted onto survey book; for two old, blind buggers with glasses the SAP is better than Suuntos in hot and steamy conditions; SAP gives you get two readings at once and you know where you are pointing it, plus electronic back up of data; SAP and Disto are lighter and more compact that Suuntos and tape.
Our accuracy wasn't brilliant: one 100m loop had a 6% closure error and a 92m loop had a 3% closure error. According to Walls the errors are mainly in the distances, so next time we'll take the distances twice to make sure the Disto is actually measuring to the target and not bouncing off the wall behind. However, the survey was good enough for our purposes.
Ouan
Charlie
New member
A few years ago I met an action photographer who used one of these devices http://www.electromax.com/fotosnipercamera.html
I means you are seadying the camera against your shoulder and with both hands so you can get a steady shot while balancing on boulders etc when you cant use a tripod.
Could a similar system [folding shoulder stock, pistol grip or similar] be set up to steady your SAP or disto? It seems to offer the stability of a tripod without the faff of setting one up at each survey station.
just a thought...
Charlie
I means you are seadying the camera against your shoulder and with both hands so you can get a steady shot while balancing on boulders etc when you cant use a tripod.
Could a similar system [folding shoulder stock, pistol grip or similar] be set up to steady your SAP or disto? It seems to offer the stability of a tripod without the faff of setting one up at each survey station.
just a thought...
Charlie
T
truescrumpy
Guest
footleg said:
Thanks for the update
menacer
Active member
Ouan said:
There are a lot of reasons why your error may have been such, but one particular thing to note, when using a disto with a regular compass clino or a pony, is that the battery from the disto will cause a magnetic shift when placed next to the compass/pony.
Wave a battery over your compass/pony and coo in awe at the swaying needle/digital reading....
Its not a major problem , just keep the disto and the compass away from each other when taking the compass reading, about 6 inches was enough (without getting it out and double checking)
cap n chris
Well-known member
Charlie said:A few years ago I met an action photographer who used one of these devices http://www.electromax.com/fotosnipercamera.html
Lol!
Someone had one of these, in a bag, a few years back (IIRC) and stopped off for a drink or two in one of the pubs in Cheddar Gorge, of an evening.
Within half an hour the place was surrounded by armed police.
D
darkplaces
Guest
The police and people are jumpy at anything these days!
Myself and another are using a laser range finder, as used in construction and a compass to survey A <secret> Quarry, results will be copyright free and published in good time. I might even write a book!
Myself and another are using a laser range finder, as used in construction and a compass to survey A <secret> Quarry, results will be copyright free and published in good time. I might even write a book!
