mapping systems

[smartbomb]

rchrds, the ulf system you describe is very similar to a pseudolite(PL). PL's are most often small transceivers that are used to create a local, ground-based GPS alternative. the concept is the same radio based ranging. like GPS you can measure fractional parts of the carrier for super precise measurements.

hopefully i will here from some of the manufacturers that i deal with this week. maybe they have some works in progress or mothballed stuff that may apply.

anyone here associated with the WKPP? i would like the get some first hand info on the whole survey process.

this whole idea started as an exercise for surveys of bridge piers and now has completely morphed into something a whole hell of a lot more interesting. being an old fart with latent ADD is a burden i must carry. i get bored very easy and my mind tends to drift into flighty concepts.

cheers
scott

[smartbomb]

god i can't help myself. has anyone looked into close range photogrammetry? essentially, 2 cameras separated by a known distance (i.e. mounted to a bar of 1 meter) can simultaneously capture an image. with some known scale present in the images, a 3d map can be "digitized" from the images. the concept is identical to the old steroscopes you would see in old western movies. it still doesn't resolve the spatial orientation, but it is an option.

from wikipedia
USBL (Ultra-short baseline) is a method of underwater acoustic positioning. A complete USBL system consists of a transceiver, which is mounted on a pole under a ship, and a transponder/responder on the seafloor, a towfish, or on a ROV. A computer, or "topside unit", is used to calculate a position from the ranges and bearings measured by the transceiver.

An acoustic pulse is transmitted by the transceiver and detected by the subsea transponder, which replies with its own acoustic pulse. This return pulse is detected by the shipboard transceiver. The time from the transmission of the initial acoustic pulse until the reply is detected is measured by the USBL system and is converted into a range.

To calculate a subsea position, the USBL calculates both a range and an angle from the transceiver to the subsea beacon. Angles are measured by the transceiver, which contains an array of transducers. The transceiver head normally contains three or more transducers separated by a baseline of 10 cm or less. A method called “phase-differencing” within this transducer array is used to calculate the angle to the subsea transponder.

USBLs have also begun to find use in "inverted" (iUSBL) configurations, with the transceiver mounted on an autonomous underwater vehicle, and the transponder on the target. In this case, the "topside" processing happens inside the vehicle to allow it to locate the transponder for applications such as automatic docking and target tracking.

[FW]

anyone here associated with the WKPP? i would like the get some first hand info on the whole survey process.

What you really need it the "older" Wakulla group, called Wakulla 2. From what I understand, the current WKPP only uses knotted line, and a dive compass to survey, and they only survey to the nearest 10 feet. They don't record passage width at all.

[smartbomb]

i figured the wkpp only because they're local to me. anyone could shed some background on the survey process. i have 16 years of "terrestrial" surveying under my belt. mostly curious as to the cross over techniques; traverses, loop closures, control marks. if compass and line are the norm, it seems fairly straight forward. but how does the higher levels of surveying get done? at the top of the scale i read the requirement is the cm level. hell i know guys that cant pull that off on dry ground. in a nutshell "traditional" surveying is getting boring. according to my 14 y/o know-it-all, i need something with a challenge so i don't turn into dull old fart.

[Squirrel Girl]

What you really need it the "older" Wakulla group, called Wakulla 2.

http://www.usdct.org/wakulla2.php

There was a first Wakulla expedition by the USDCT. Then there was the WKPP. Then the USDCT went back for Wakulla 2. The WKPP were invited, but chose not to participate. And now it's back to being WKPP at the park again.

[Arnold Mesiser]

http://www.usdct.org/wakulla2.php

There was a first Wakulla expedition by the USDCT. Then there was the WKPP. Then the USDCT went back for Wakulla 2. The WKPP were invited, but chose not to participate. And now it's back to being WKPP at the park again.

It's amazing how much cutting edge and NEW technology was created at or for the project.I still find the dives fascinating to this day -so MUCH more was done for cave science and diving rather than simply worrying about EOL

[Webmaster]

Jason you might be able to use a ULF system like that for triangulation. But I don't think it would work too well as a GPS type setup. GPS is all based on timing, and of course the time that signal takes to travel from the satellite to the receiver is fairly constant because it's travelling through the atmosphere.

Underground it's going to be travelling through a much greater variety of materials, and even small variations would cause the position to be off.

Acoustic systems designed for open water environments are unlikely to work in a cave as-is because of all the reflections.

If you just had two devices that worked line of sight, that could talk to each other that would work. Collect depth, orientation to the other device relative to magnetic north, and range to the other device at each station. Maybe a low powered ULF transmitter/receiver that was very directional.

[apitkin]

Andy is correct- this could very well act as a base module, providing a compass (possibly not accurate enough, and limited in vertical axis measurements, I will find out next month) a digital depth measurement, and a processor. Whether or not the processor is up to what you are going to ask of it is another discussion. Of course, you would have to integrate an additional module (ala the X-Link) that would receive and process ULF signals, add a 3rd accelerometer for measuring vertical angle, and then some way of transmitting your data from the mapper to the unit.

Probably this makes little sense to have it all separated and be forced to integrate multiple data transmission links rather than to have it all located on one board, with the calculations made in a single processor and program, and all of the data transmission hardwired.

Jason

Eric at Liquivision tells me that the compass is very accurate indeed, just that the current deco software doesn't use it effectively to achieve that accuracy. The accelerometer can measure vertical angle. Also, the processor is far more powerful than (I believe) any other dive computer, which allows the use of the free GNU compiler which produces relatively slow code. I got the impression from talking to him that even using inefficient open source tools, the X1 had plenty of processing headroom when doing deco calculations. Decosoft, for example, computes two models simultaneously. And that doesn't include for the potential performance improvement using efficient compilers (=$$$, of course). I doubt that the necessary calculations for a location system would be much more processor-intensive.

I agree it's better to have it all on one board, but with the X1 you have a very compact, powerful, underwater computer with plenty of storage memory, a great screen, an accurate compass and depth gauge, and a means of hardware expansion. It might be a good place to start.

My concern about the ULF idea is based on (my understanding of) simple physics. With low frequency comes a long wavelength. That long wavelength will necessarily limit the spacial/temporal resolution of the signal, and therefore the accuracy of location. I'm not sure how low the frequency needs to be, nor how to calculate exactly what the limit of resolution will be. I haven't opened a physics textbook in a long time, so I could be completely wrong.

I hope so, because it's a great idea.

Andy

[jdz]

Hi guys, just been alerted to this thread..

I have been interested in various mapping techniques for some time.. Initially I had a ULF transmitter and receiver built very similar to Pearse's unit, but it was able to receive a surface signal once the position was located from above, hence we could move on to a subsequent point and hence gather many points on the same dive. this system was used at the same time as my collegue was using his "pinger". In this way we completed the entire resurvey of our well known Tank Cave here in OZ with nearly 8 klms of passage.
see... http://www.cavedivers.com.au/articles/thumper.htm and... http://www.cavedivers.com.au/articles/pinger.htm and... http://www.cavedivers.com.au/articles/mapping.htm

We have also continued mapping using the simple tape & measure along the line, knowing that we had fixed known points to return to.. http://www.cavedivers.com.au/articles/history.htm

From here, we have moved on to create 3D models by using meshing software and have created a model of our Piccaninnie Ponds which I'll try to add a link to in a day or so.

I am currently finishing the housing for a "disto2" http://www.buybrandtools.com/acatalo...-Disto-D2.html and will be testing this in the next week or so and can report back on this also..

I always thought that I would like to built a system similar to that described above, where we could drive 3 or 4 spikes into the ground positioned around a paddock and set up an artificial underground satellite system using ULF signals and then reprogramming a gps to receive these signals and hence reference itself u/w accordingly...

and finally another idea which will be trialled soon.. one diver with a paddle or similar object in front of a 2nd diver with camera at a known approx distance and multiple photos taken say every 5 metres along the lined passageway, then "mesh" the photos together to produce wall outlines using the paddle as a reference measure, thus collating multiple data points (similar to digimapper, but much less expensive..)

anyway, enough rambling.. cheers,

JDZ

[FW]

...and finally another idea which will be trialled soon.. one diver with a paddle or similar object in front of a 2nd diver with camera at a known approx distance and multiple photos taken say every 5 metres along the lined passageway, then "mesh" the photos together to produce wall outlines using the paddle as a reference measure, thus collating multiple data points (similar to digimapper, but much less expensive..)

anyway, enough rambling.. cheers,

JDZ

That might work in very clear water. There are many caves with low visibility.

Say hello to Ken Smith for me