GroundquestMSA wrote: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