How long is that cave-Really?!

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Re: How long is that cave-Really?!

Postby George Dasher » Aug 28, 2009 3:03 pm

Well, I get confused pretty easy myself sometimes...
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Re: How long is that cave-Really?!

Postby Jeff Bartlett » Aug 28, 2009 4:03 pm

Obviously this quality illustration needs to be included in the upcoming (right? please?) revision of On Station.
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Re: How long is that cave-Really?!

Postby Cheryl Jones » Aug 28, 2009 9:30 pm

Jeff Bartlett wrote:Obviously this quality illustration needs to be included in the upcoming (right? please?) revision of On Station.


Please George, say "yes"!! :pray:
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Re: How long is that cave-Really?!

Postby trogman » Aug 29, 2009 8:28 am

George Dasher wrote:You all are making this way too difficult.

Bob Thrun is correct; you can't argue with the survey tape.

If the tape says the cave is 100 feet long, then the cave is 100 feet long, no matter what the slope of the tape.

Thus a vertical 100-foot-deep, dead-bottomed pit is a cave 100 feet long.

Another example would be holding up a yard stick at many different angles. The yard stick is still one yard long, no matter what angle it is held out.

Thinking horizontal distance for a cave length only confuses the issue. It is best just to mentally delete horizontal length from the entire process. It doesn't count for anything.

And there is an offical document for this. It was described in the January 1981 NSS Bulletin.

:bat sticker:


I certainly wasn't trying to make it difficult. It's just that I was mapping a new cave, and on my maps I generally have a place in the title block (or whatever you call it) where I put "Cave Length: xxx' " . In the past I had always omitted the vertical parts from this number, and put them in a separate listing in the title block, stated as "x pit(s) xx' deep." After several discussions with fellow cavers, and also after reading On Station, I got to wondering if I had been doing it correctly. As I stated before, some cartographers I have spoken with still use this method. This same question also applied to the cave length number one turns in to the state Cave Survey listing.

George Dasher wrote:Well, I am confused--because I no longer understand what we are "arguing about."


I don't think I would call it an "argument," at least not yet. As I stated above, I'm just trying to determine what number (if any) I should put in the title block on my maps. And also, what number I should turn in to my local state cave survey group. I guess that may vary according to state. Part of my point was that (at least from what I can tell) this has not been clearly defined by the state surveys that I have dealt with.

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Re: How long is that cave-Really?!

Postby Aaron Addison » Aug 31, 2009 9:34 am

This one is easy.....

Instead of putting "cave" in your title block, just put "surveyed" length (after all isn't implied already that the length refers to the cave?). Same for vertical, just put "surveyed" depth.

To suggest that you have any other information than what you surveyed for horizontal or vertical extent is likely not accurate.

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Re: How long is that cave-Really?!

Postby Spike » Aug 31, 2009 11:22 am

I only have one comment concerning the historical use of True Horizontal Distance THD being reported on a maps. I use surveyed length by the way. We've all been on surveys where one station may be on the floor and the next on the ceiling, or wall, then the next was back on the floor, and so on, in what would otherwise be a horizontal passage. I believe that cartographers was felt that the raw total of the survey shots was an exageration and that the THD more accurately described the traversable length of the cave. In the Salem Plateau on MO the caves are often of such a horizontal nature(no pits to speak of) that they encouraged this reasoning.

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Re: How long is that cave-Really?!

Postby ian mckenzie » Aug 31, 2009 12:01 pm

Caves are never exactly as long as data says they are. Statistics are only indicators of true length, and provided everyone surveys to the same standards they provide a means of comparability. To that end, most cavers worldwide use the exact surveyed length as an indicator of a cave's extent. Surveyed depth, on the other hand, is a true measure and not an estimate.
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Re: How long is that cave-Really?!

Postby trogman » Sep 5, 2009 6:42 am

Aaron Addison wrote:This one is easy.....

Instead of putting "cave" in your title block, just put "surveyed" length (after all isn't implied already that the length refers to the cave?). Same for vertical, just put "surveyed" depth.

To suggest that you have any other information than what you surveyed for horizontal or vertical extent is likely not accurate.

AA


I like the idea of using "surveyed length." That should be clear enough. As far as vertical extent goes, that is a fairly straightforward statistic that most people understand the meaning of. I think I will continue to list the pits and their depths separately. I think that's a valuable piece of info to have on a map; it lets the prospective caver know right away approx. how much rope they might need. (if any)

Thanks for all the input and suggestions!

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Re: How long is that cave-Really?!

Postby anti-jeff » Jun 24, 2010 12:09 pm

Sorry to drag up a rather old topic, but this seemed the most appropriate place to put my question.

From what I understand vertical extent should be the vertical difference between you highest and lowest station. So if you're lowest survey station is 20 feet below your 0.0 datum, and the highest is 20 feet above your 0.0 datum, the vertical extent is 40 feet. Right?

My question is this: I'm drafting a cave where the survey station for the 'highest' station is on the floor with a decent amount of passage height, while the survey station 'lowest' station is on the ceiling. Currently the number I use for vertical extent comes from Walls (Project > Review > Segments tab > Details/Rprts > Depth... I see there is also a vertical length, any idea what the difference is?)

The problem is, the number I'm getting doesn't seem to do justice to the actual 'height' of the cave. I'm getting 5 feet when really the cave is about twice the number from the highest ceiling to the lowest floor.

Is it possible to consider vertical extent to be from the 'top' of the cave (suvery station + U from LRUD) to the 'bottom' (survey station + D from LRUD) of the cave? Is this done? If not, why is it a bad idea? I'm kind of new at all of this and want to learn, so I'd appreciate any insight y'all have about this :)

Here's a picture of a hypothetical cave to illustrate my point. Click on the image to view a larger version.
Image
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Re: How long is that cave-Really?!

Postby Jeff Bartlett » Jun 24, 2010 12:26 pm

anti-jeff wrote:Sorry to drag up a rather old topic, but this seemed the most appropriate place to put my question.

What, no "How deep is that cave-Really!?" topic?
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Re: How long is that cave-Really?!

Postby trogman » Jun 24, 2010 2:28 pm

It is interesting to see this old topic revived, especially since I have had a lot more dealings with this topic since then. In regards to the question about vertical extent, the method you suggest makes perfect sense to me, but of course that is just my opinion. There are really no official constraints in the world of cave surveying, since there is no governing body. I have had similar questions myself, especially when it comes to using ceiling heights measured with a laser. If I go into a generally horizontal cave, and in the back of it is a 50' dome (as measured with a laser), then should I count that 50' toward the vertical extent? I see no reason why it shouldn't, but perhaps someone more knowledgeable than myself will weigh in on this question. I wouldn't count the dome as part of the "surveyed length," unless I actually climbed it. But vertical extent is something different, at least from my perspective.

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Re: How long is that cave-Really?!

Postby Anonymous_Coward » Jun 24, 2010 2:56 pm

anti-jeff wrote:Is it possible to consider vertical extent to be from the 'top' of the cave (suvery station + U from LRUD) to the 'bottom' (survey station + D from LRUD) of the cave? Is this done? If not, why is it a bad idea?


I don't know what the according to Hoyle (or Dasher, or Kambesis) gospel is on this, but I can tell you that I have done this on a cave map for exactly the reason you described. The survey stations were lying about the cave depth, so I included the LRUD depth.

I don't know if this is considered kosher, but it certainly makes sense to me. On top of that, the map I did it on was scrutinized by the NSS/UIS high priesthood of cartography and won an award.
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Re: How long is that cave-Really?!

Postby trogman » Jun 25, 2010 6:40 am

After re-reading the original question, and the replies posted by myself and others, I wanted to add one caveat to what I stated: If the LRUD is done the old-fashioned way (guesstimated), then I do not believe it would be proper to use that ceiling height in figuring the vertical extent. However, if it is done with a measuring device, such as a laser, then it would be considered as reliable and should be included. Just my opinion, as always. Still waiting for the "experts" to weigh in, but until then us novices will throw out our opinions. :shrug:

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Re: How long is that cave-Really?!

Postby George Dasher » Jul 1, 2010 2:55 pm

Cave depth is more accurate than cave (or survey) length, but neither numbers have repeatable accuracy. So there is no sense in stressing to the Nth Degree over either value.

My suggestion is that, if you really feel a more accurate depth can be achieved by including the passage height of the last station, then to go ahead and do it. But I have to admit that a better option is to realize the problem while in the cave and take a last shot to the lowest (or highest) point in the cave.

My suggestion is also a general rule. I won't use it all the time, particularly if there is a high dome near the top of the cave. I think it is better in those cases to use trig or a laser to calculate or measure the height of the dome.

And second of all, I really don't care if the cave can be made a small distance longer or "more vertical." To repeat, these values are not repeatable. (Yes, I enjoyed that pun!)

I really don't feel there are any hard-fast rules in cave surveying, other than to reduce the data and draw the map as soon as you get out of the cave.
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Re: How long is that cave-Really?!

Postby rchrds » Oct 19, 2010 11:11 pm

The TCS considers total vertical extent to include U of LRUD of highest station to D of lowest station. The best answer is to use a disto and create a vertical station at your highest and lowest points if that is a concern.

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