Slashdot Mirror
Technology for Mapping the Underground?
Archon-X asks: "As an avid CaveClanner, I spend my spare time sloshing around underground in drains, and have more than once considered 'mapping' the drains. How would readers approach this problem? Mobile reception and presumably GPS is non-existent, and it's pretty dark and wet down there."
You could try using inertial navigation.
.... sorry, it's confidential information. :-)
There are some highly sensitive solid-state accelerometers. I believe that they are manufactured by National Semiconductor. Microsoft uses them in their handheld Sidewinder FreeStyle Pro. They look like fat silicon chips and the interfaces are digital, so they are easily connected to microcontrollers.
If you need higher precission, you could add gyroscopes. Laser gyroscopes are popular this days and their prices have come down quite a bit.
When you combine accelerometers with gyroscopes and a fairly high sampling rate, you can obtain high degrees of accuracy and precision.
If you can use waypoints, then you can calculate drift rates and improve accuracy. If you think that the GPS signal may be usable then you can use a GPS receiver as a waypoint source.
From my experience, the most common source of errors is high frequency content, specially when walking. A damper would go a long way towards improving the accuracy.
You should have no problem integrating everything into a small backpack with a laptop (if you need a UI), or a small shoe box if all you want is data logging.
Hope this helps, if you want more information such as part numbers and suppliers, I could gather some. As for designs and software,
Hector
To map a maze of twisty passages, all alike:
What you'll need: Pen and paper, and lots of objects (at least one for every room).
What to do: Drop an object in the first room, which we'll call room #1. Make a note of what object you dropped in room #1 (let's say it's a sword). Put a '1' on the paper, with eight lines coming out at the compass points. Pick one at random (let's say north) and go that way.
You'll be in another room, which we'll call room 2. Drop another object (say, a bell), and make a note. Put a '2' on the paper, with eight lines coming out at the compass points. Finally, put a little '2' next to the line from room 1 you used to get here (in this case, north). You now know that going north from room 1 leads to room 2. Pick another direction (say, north again), and continue.
If you end up in a room without an object, it's a new room, and you repeat the instructions above. If it's a room containing an object you dropped, then you just need to make a note on the appropriate line from the old room. Pretty soon, you'll have the whole maze mapped.
Unless the thief comes by and picks up some of your objects. That'll mess you up. I recommend killing him first.
I've mapped many a storm system, and here are a few quick tips.
1.A compass works well in older systems composed of brick or clay tiles. Concrete pipe and box culverts often have enough iron in them to really mess up your compass.
2.Most cities have "Atlas sheets" available for all city utilities. Water, storm, and sanitary are often listed on the same sheet. You can usually find these at the municipal utility complex - for free. Just tell the clerk at the counter you are doing a topographic survey for new development, and need to show such on your plot.
3.I have used a cordless drill, concrete bit, and concrete screws to set points in the ceiling of pipes, at angle points. Use string and a protractor to measure angles. The screw also provides a nice hook to pull tape distances with. There is no way I'm taking a 20 grand total station into the sewer!
4.Put the tip and straw from a can of WD-40 on a can of funky coloured spray paint. Use the straw to spray out of the manhole lid. This can help you tie your underground survey in with aboveground locations.
5.Always be thinking like water. Water flows downhill. (duh) You aren't going to find that 10 foot dia. pipe very far from the local river or stream, or whatever your natural drain is. Take a johnboat or raft or such on a slow paddle down the riverbanks, looking for the big outlet pipes, and start your adventure there.
6.Methane or carbon dioxide poisoning is NOT a major risk in STORM sewers. Watch it in older systems, though. Many of the older ones are combined - still. If there is organic debris on the floor of the pipes you are exploring, that is also a cause for alarm about gas. Clean bottom storm pipes are almost always safe.
Those who said they have used GPS anywhere underground, near a lid or not, are full of it.
Who wants to carry a 4' level in the drains? What will you do with it? If you want to measure slope - get a combo compass/inclinometer or fancy yourself one out of the protractor you are using to measure bends.
Only one way to map a storm system - old school two man. Measure the angle and chain the distance!