How to survey/sketch corkscrew shaped passage?

[GroundquestMSA]

I'm trying to survey a cave that includes an intermittently vertical spiral. A 30ft. drop, followed by a left turn and 20ft. of steep slope, followed by a left turn and a 10' drop and 25ft. of steep slope, followed by a 15' drop and a left turn into continuing passage.
I'm having difficulty getting an azimuth because of the vertical difference between stations. I can get a few using a plumb bob and backsighting, but there are a couple of stations that I can't place over a free hang. Any tips?
If I ever get the data, how do you all suggest sketching this sort of passage? Is there any way to represent the passage in the plan view? I thought of making two profiles from east-west/north-south to augment the plan but I am unsure how to do so. I am plotting and sketching everything by hand. Do most mapping programs allow one to view the line plot from different angles?

[rchrds]

I'm trying to survey a cave that includes an intermittently vertical spiral. A 30ft. drop, followed by a left turn and 20ft. of steep slope, followed by a left turn and a 10' drop and 25ft. of steep slope, followed by a 15' drop and a left turn into continuing passage.
I'm having difficulty getting an azimuth because of the vertical difference between stations. I can get a few using a plumb bob and backsighting, but there are a couple of stations that I can't place over a free hang. Any tips?
If I ever get the data, how do you all suggest sketching this sort of passage? Is there any way to represent the passage in the plan view? I thought of making two profiles from east-west/north-south to augment the plan but I am unsure how to do so. I am plotting and sketching everything by hand. Do most mapping programs allow one to view the line plot from different angles?

No real suggestions on taking the data other than making sure that you take backsights, as your initial sights are sure to be off, of course there are tricks to reading high angle azimuths (sight through the eyepiece, with the light on the far station just below the eyepiece, so you can use the same eye to view both the light and the azimuth) the uphill back-azimuth is harder to do.

As for the sketching- it is imperative that you consider how you are going to draw the final map before you start on the sketching. For the plan view, consider doing it in pieces, so that no passage is obscured by passage above it- make multiple, to scale, segments of the plan view, so that you can get all of the floor detail in on the sketch. Then, pick your profile views (as it sounds like you did) and sketch profiles/cross sections on those axis along the passage, so that you can have accurate representations on the final drawing.

Once you come to the final drawing, though I'm guessing on how the passage works, inline with the passage leaving the uppermost and lower most sections, you draw the floor details for the uppermost piece of passage (before it loops under itself) and then if possible, show the hidden lines, or just the outermost extents of the lower passage. Then, aside that, you might show your sections of plan view, oriented correctly with your map, in slightly darkening shades of background color to indicate increasing depth, with connection lines that indicate where each piece ties together. Then you would have to show your two major cross-sections in a similar fashion somewhere nearby. This might be easy if it is a single passage cave, or just a small feature in a non-maze cave, but you might be squished for room in a cave with lots of other passage nearby.

Another option might be to show an extended profile of that section of the cave with the hash marks indicating the start and finish of your extended profile. This might be the easiest way, as it might not be immediately obvious to the caver that you are corkscrewing as you are descending, and it will be easier to show all the drops and details this way. This will necessitate accurate LRUDs (laser measured ceilings) to make the map look right.

Jason

[chh]

Getting into a position where you can sight both of the stations at a better angle is a good tip, but it may not always be possible.
A couple of other ways to do it are these, assuming that your passage is as you described, corkscrewing down as you go:

Pull the tape from the higher "A" station to the lower "B" station and release the tension on it so that there is a free hanging drape in the tape itself. Now take a backsight from B station to A station, sighting on where the tape hangs. This only really works on shorter slopes and in passage where there isn't significant air movement. You can also incorporate a plumb bob or weight in this scenario for a more accurate reading. Pull the tape from A to B and put a plumb bob or weight towards the lower third of the tape, or wherever you can see it to take a reading. Now release the tape from the B station and sight again on the tape itself or on the plumb bob/weight. This will help mitigate air movement or any crooks or bends in your tape.

Also, just because you may not be able to get a plumb bob on your A station, doesn't mean you can't use one. You can also survey in a stairstep method. If the passage allows you to get to the walls/ceiling of the corkscrew or slope, take a reading from your A station to a place across the passage on the wall or ceiling where you can get a plumb bob to. Take your azimuth/inclination. Now hang a plumb bob/weight from B station. Find the point on the floor where the plumb bob lands, or a point along it that isn't the floor(this takes a little more pre planning/finagling) This is now C station in your book but it has the same azimuth as B station, but with a -90 on the inclination. Continue this stair stepping if necessary. Azimuth frontsights are taken to B station (obviously) and if you can get to a point where you can see both A and C station you can shoot a backsight along the plumb line. Be careful how you record this data, however because it can confuse the line plot program as your back sight went from C to A station, bypassing B. If you record it in this way the computer won't like you. Make sure that the backsight azimuth goes with B station and the inclination is +90.

Also, this may be obvious, but you can also lift or shift where you take your measurements. If you can't take a good measurement directly at the station, for an azimuth you can take a measurement directly over or under your point without sacrificing accuracy as long as you are truly under or over it. For an inclination you can measure from left or right of your station without compromising accuracy, again so long as you can be sure you are directly left or right.

Hope I explained all that well enough. Good luck!

[John Lovaas]

I'm trying to survey a cave that includes an intermittently vertical spiral. A 30ft. drop, followed by a left turn and 20ft. of steep slope, followed by a left turn and a 10' drop and 25ft. of steep slope, followed by a 15' drop and a left turn into continuing passage.
I'm having difficulty getting an azimuth because of the vertical difference between stations. I can get a few using a plumb bob and backsighting, but there are a couple of stations that I can't place over a free hang. Any tips?

You mention the plumb bob- if it's at all possible, set your survey line through the passage using a combination of vertical shots, using your plumb bob- or tape, to determine convenient/safe from/to stations, and short horizontal shots. Think of a staircase viewed in profile, with long 'risers' and short, relatively level, 'landings'.

If I ever get the data, how do you all suggest sketching this sort of passage? Is there any way to represent the passage in the plan view? I thought of making two profiles from east-west/north-south to augment the plan but I am unsure how to do so. I am plotting and sketching everything by hand. Do most mapping programs allow one to view the line plot from different angles?

For your in-cave sketching- keep it simple and neat. Don't worry too much about sketching the plan view data as a single continuous segment- sketch each shot as an individual segment, then work on assembling the individually sketched shots when you are back home. Same goes for the profile view; sketch each profile shot as an 'extended' view- that is, your point of view is perpendicular to the survey line.

Plotting the plan and profile survey lines by hand would be a trigonometric nightmare- but if you're a steampunk aficionado, knock yourself out! ;-) Both Compass and Walls will generate plan and profile views that can be viewed from any point in space. Both programs are fully functional as free downloads, and Compass is quite easy to learn- I entered data and generated 2D and 3D plan and profile views within an hour of downloading it, back in the 1990s. At that time, my computer skills were sufficient to start the computer and log onto my email account- no special skills whatsoever.

For your plan view, both cave survey programs can assign elevations (relative to your entrance datum, or any station that you otherwise choose) to each of your survey stations. In a plan view, you can indicate elevation at various points along the passage- giving the map reader a sense of how the passage trends. The profile view would be more intuitive, and you should include a simple scale bar next to the profile view to help the map reader.

[Bob Thrun]

I had an article on surveying vertical caves in Nylon Highway 20.
http://www.caves.org/section/vertical/nhback/NH20.pdf
Much of this material was included in On Station. I only covered making instrument readings, not sketching or map layout.

Dwight Livingston did a very good job of showing vertical corkscrews on his map of Shovel Eater Cave. It won the medal at this year's NSS Convention. He selected the angle for the profile and made trips to sketch a profile at that angle. Multiple levels were done using call-outs: the combined levels, the top level, the next level down, etc.

[GroundquestMSA]

I had an article on surveying vertical caves in Nylon Highway 20.
http://www.caves.org/section/vertical/nhback/NH20.pdf

Thanks for the help. I was supremely satisfied to read the following in your article in reference to a hanging tape blowing around: "Just guess the bottom as best you can. Cave surveying does not have to be super-accurate."

Whether or not you still feel that way, I am comforted by the fact that someone at some point had such a reasonable view of the matter.

[LWB]

For the survey, borrow a Disto X (just make sure it is calibrated) - it does those steep angle shots with ease. Of course the poor sketcher will not be happy with the speed of the survey...