Best way to locate points on surface above a cave?

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Best way to locate points on surface above a cave?

Postby JP McLendon » Jun 2, 2014 3:59 pm

I would appreciate any suggestions regarding the best (easiest, quickest) way to locate points on the surface that directly overlie survey stations in the cave. For example, suppose we find a place in the cave with surface debris and would like to examine the surface directly above for an entrance or dig. The ideal solution would allow me to input surface survey data in the field using a laptop and would generate an azimuth and distance from the last station to the desired point. I've sometimes overlayed the cave map or lineplot onto a topo or satellite image to identify the general area, but I'm looking for a much more precise solution. I primarily use Therion for data processing and map making, but I'm unaware of how to easily accomplish this with Therion. Currently, I temporarily rename the last surface survey station to the name of the station I'm trying to get above. This tells Therion that I've closed a loop and it will give me the closure error in all three axises. This accomplishes the goal, but it is subject to blunders and overly time consuming. I'm hoping to find a better way, perhaps through some function of Therion with which I am unfamiliar or through one of the other cave mapping programs.
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Re: Best way to locate points on surface above a cave?

Postby GroundquestMSA » Jun 2, 2014 5:02 pm

I'm usually too impatient to do quality surface survey, but I have used surface survey to locate surface features that correspond to in-cave breakdown. How precise are you talking?

I simply use a scale and protactor to measure the azimuth and straight-line distance from the entrance to the in-cave feature in question. Then, with a couple of stakes and a calculator, I survey the surface, sticking to the pre-determined azimuth, correcting the horizontal distance as I go with clino and calculator, until I've gone the pre-determined distance. This method has twice dropped me perfectly into sinkholes above breakdown. I suppose though, seeing words like "Therion" and "closure error", that you're looking for a better and fancier solution. My sinks were only a few hundred feet from the cave entrance.
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Re: Best way to locate points on surface above a cave?

Postby Extremeophile » Jun 2, 2014 5:15 pm

I'm not specifically familiar with Therion, but other data reduction programs such as Compass and Walls allow you to enter a geo-reference point, such as the entrance, and then will give you the coordinates and elevation for any survey station in the cave. The accuracy of finding this location on the surface will be a function of the accuracy and precision of your entrance location, cave survey data, and surface locating technique (e.g. GPS). For most cave surveys, and standard GPS technology, this should get you to within ~100' or less. If you're going to then go to the trouble to dig, most people would first conduct a radio location. In your post you say "best (easiest, quickest)". The easiest and quickest won't be the most accurate, so there are unfortunately trade-offs.
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Re: Best way to locate points on surface above a cave?

Postby lleblanc » Jun 2, 2014 10:45 pm

Extremeophile wrote:I'm not specifically familiar with Therion, but other data reduction programs such as Compass and Walls allow you to enter a geo-reference point, such as the entrance, and then will give you the coordinates and elevation for any survey station in the cave.


Auriga will let you "walk" the cave from the surface, with a cross on the PDA screen following the current GPS position against the cave map in plan view (connect your PDA to a Bluetooth GPS). Upcoming version will also show current altitude against the cave map in profile view.
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Re: Best way to locate points on surface above a cave?

Postby Martin Sluka » Jun 3, 2014 1:29 am

Wuith all respect:

If there is a surface breakdown the most accurate way is to use method named "radiolocation". In the simplest way you may use avalanche transceivers. Check:

http://caves.org.uk/radio/bookinfo_02.html
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Re: Best way to locate points on surface above a cave?

Postby Martin Sluka » Jun 3, 2014 3:32 am

Repost from Bruce Mutton on Therion mail conference:

As a hack, how about temporarily making the survey station near the debris an entrance. Then an export to a cave-list will give you the coordinates directly.
Eg
export cave-list \
-location on \
-surveys off \
-output ../Output/MiddleEarthcaves.html

Or of you use .kml extension you get a Google Earth file directly. (note m.s.: in kml file there are coordinates too)
I’m assuming you want the easiest way to walk to the surface location directly above the cave, and have a gps unit into which you can enter these as way points. Re-reading you question that might not be what you want.

There might be other approaches using continuation flags, and or obtaining the coordinates from an sql export or from a model export to .3d and use Aven to obtain coordinates.
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Re: Best way to locate points on surface above a cave?

Postby Leclused » Jun 3, 2014 6:44 am

Martin Sluka wrote:Wuith all respect:

If there is a surface breakdown the most accurate way is to use method named "radiolocation". In the simplest way you may use avalanche transceivers. Check:

http://caves.org.uk/radio/bookinfo_02.html


Avalanche tranreceivers will work well when the difference between the tranceivers is not too big (estimation 10-15m). For a bigger differnce in distance you can use an indcution loop.

More info about the indcution loop : http://www.scavalon.be/avalonuk/technical/loop.htm

BR

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Re: Best way to locate points on surface above a cave?

Postby LukeM » Jun 3, 2014 2:16 pm

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Re: Best way to locate points on surface above a cave?

Postby lleblanc » Jun 4, 2014 10:26 am

LukeM wrote:Radiolocator kits:
http://radiolocation.tripod.com/


But before attempting radiolocation, you need to have a fairly good knowledge of where the surface overlies the cave. I think this was the original poster's quest. After that this surface position can be refined with radiolocation.
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