cross-section technicalities

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cross-section technicalities

Postby KeyserSoze » Jul 30, 2011 7:26 pm

The following question has raised some discussion amongst fellow cavers and I was hoping to get more input to resolve the matter.

I think this can be resolved easily with a technical answer to explain exactly what each of the tick marks represent. Is the tick mark on the plan view supposed to represent the actual position that the caver stood when drawing, which therefore cannot be altered; or could it be used to represent a hypothetical position, (IF you were facing this direction, then you would see this), which would allow for it to be flipped in either direction on the final map? Also what about the tick mark on the cross-section side of the map, what does it indicate?

So given the following surveying scenario, which one or more of the following examples would be a correct way to represent the cross section on the final map?

A caver draws a cross section at station P2 while he faces the next survey station at P3.
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Re: cross-section technicalities

Postby Dwight Livingston » Jul 30, 2011 9:09 pm

What you call a "tick" I'd call an arrow. In mechanical drafting an arrowhead is placed on that arrow. Cave cartography dropped the arrowhead at some point.

Only C makes any sense to me. All your sections appear to show a view facing north. In C, the arrow on the left end of the section line is pointing north, indicating that the section is drawn facing north. That matches. In all the other sections, that arrow is pointing south, which doesn't match the section.

When I use letters to identify a section, I'll put arrows on both ends of the section line. In that case, both arrows point the same way, both are placed in the context of the plan view, and both indicate an azimuth.

When I use the section line as a leader to the section view, as you have shown, I don't add an arrow beyond the section. I've seen it done, but I couldn't tell you what it means.

I would take a section drawn in a sketch facing, say, south and flip it to face north in the map. I don't see any reason not to.

I'll be interested to hear what others consider proper.

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Re: cross-section technicalities

Postby trogman » Jul 31, 2011 10:21 am

I would second what Dwight said above. In my experience with mechanical drawings section views are usually very easy to interpret because the arrows at the ends tell you which way you are looking toward. The same applies to cave cartography, except that the arrows are replaced by a simple tick mark(as you called it). The direction that the end of this line points is the direction you are looking in the section view.

I am currently working on a map with a whole page devoted to section views. The cave has a lot of vertical elements to it so in order to allow them to be depicted correctly, I decided to do it this way. It does tend to complicate the transfer of measurements, though.

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Re: cross-section technicalities

Postby Extremeophile » Jul 31, 2011 10:45 pm

Dwight Livingston wrote:When I use the section line as a leader to the section view, as you have shown, I don't add an arrow beyond the section. I've seen it done, but I couldn't tell you what it means.
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I also don't use an arrow next to the x-section. The majority of maps I've looked at include this second arrow and it always points up. Since I can't imagine drawing a x-section in any other orientation except the top of the page being up, this arrow seems unnecessary.

I drew a couple early maps with an actual arrow on the side of the passage opposite the x-section because I thought it made the map more intuitive to people unfamiliar with reading cave maps. I had so many people (cavers) tell me that the arrow head was redundant that I've stopped using it, as is common practice, and now just use the "tick" mark.

I choose to orient x-sections in one of two ways, and the choice of which method depends on the cave and passage. I either orient them facing the way a caver travels into the cave, or facing generally towards the top of the page (usually north, but not always).
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Re: cross-section technicalities

Postby batrotter » Aug 1, 2011 4:55 am

"C" is the correct way to show the cross section. As others have stated, the line forms the cutting plane and the arrowheads ahev been omitted but they do show the direction that you are looking. A survey station was set at that particular cross section.
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Re: cross-section technicalities

Postby ian mckenzie » Aug 1, 2011 11:49 am

There is undoubtedly a documented, proper way to do things, but up here we generally only use one 'tick' or arrow to indicate the direction of view. The line through the cross-section indicates the horizontal plane of the cross section.
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Re: cross-section technicalities

Postby Crockett » Aug 1, 2011 3:22 pm

ian mckenzie wrote:There is undoubtedly a documented, proper way to do things, but up here we generally only use one 'tick' or arrow to indicate the direction of view. The line through the cross-section indicates the horizontal plane of the cross section.


Concur:

http://www.carto.net/neumann/caving/cave-symbols/

Of course "proper" in this sense is a slippery proposition.
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Re: cross-section technicalities

Postby KeyserSoze » Aug 1, 2011 9:59 pm

Thanks for the replies. I think I've been using the wrong terminology so I'll clarify. It seems like the "tick" mark represents only the horizontal plane, but then there's also the "arrow" that goes with them. I understand the arrow on the plan view represents the direction of view, but what does the arrow on the cross-section side represent?

What started this whole argument was asking which side of the cross section should the rock be on, left-side or right-side? So between example B and D, which one is correct?
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Re: cross-section technicalities

Postby Extremeophile » Aug 1, 2011 11:18 pm

KeyserSoze wrote:Thanks for the replies. I think I've been using the wrong terminology so I'll clarify. It seems like the "tick" mark represents only the horizontal plane, but then there's also the "arrow" that goes with them. I understand the arrow on the plan view represents the direction of view, but what does the arrow on the cross-section side represent?

What started this whole argument was asking which side of the cross section should the rock be on, left-side or right-side? So between example B and D, which one is correct?

Diagram D is the most accurate for a caver facing from P2 to P3 (i.e. facing south). The cross section, rock location and arrow are consistent. Diagram C is also acceptable for a caver facing from P2 to P1 (facing north; mirror image of cross section in diagram D). Again, the arrow or "tick" mark next to the cross section almost always points up (from the cavers perspective), but this arrow is not necessary, and in my opinion adds confusion.

You mention the tick mark possibly representing where the sketcher was standing. I'm not sure what you mean by this since it's outside the boundary of the passage.
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Re: cross-section technicalities

Postby ian mckenzie » Aug 2, 2011 12:49 am

KeyserSoze wrote:I understand the arrow on the plan view represents the direction of view, but what does the arrow on the cross-section side represent?

Nothing. The arrow, tick, pointy-thing or whatever you want to call it only relates to the Plan, showing the direction of view. To me, your examples B and D are nonsensical because the pointy-things go in both directions; if one is supposed to relate to the cross-section sketch, then it must be pointing either up or down, right? Which is nonsense.

Extremeophile wrote: the arrow or "tick" mark next to the cross section almost always points up (from the cavers perspective)

I have never seen a survey with cross-sections using an arrow indicating which way is up.

Only example C makes sense to me; sometimes you see the cross-section lines with two pointy-things in the same direction - redundant, but harmless.
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Re: cross-section technicalities

Postby batrotter » Aug 2, 2011 5:25 am

KeyserSoze wrote:What started this whole argument was asking which side of the cross section should the rock be on, left-side or right-side? So between example B and D, which one is correct?



Neither B or D are correct. The only correct example is C.
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Re: cross-section technicalities

Postby HKalnitz » Aug 2, 2011 6:51 am

I'll weigh in with what I have been telling others - this only has the weight of inertia of what I have been saying for years and not an established standard, but I have been consistent over that time:
1) the tic (or arrow) on the plan side is used to show the direction the sketcher was facing when drawing the cross section (or the viewer of the map when viewing the passage).
2) the tic on the cross section side shows the Vertical orientation of the cross section, typically pointing upwards.

Discussion:
1 - what is the right way to sketch a cross section? We almost always draw them facing in the direction of travel of the survey. This typically works out to travel farther into a cave, but not always. So how would we show this on a map? in complex maps the passages go in every differnt way, and a cartographer is faced with the fact that from survey to survey the orientation could be different. And in loop passages, two cross sections, very close to each other can be skeched in opposite orientations (at the beginning and end of a loop passage) in the SAME survey. A smart cartographer does not lay down the law, knowing it is easier and quicker for the sketcher to draft exactly what they are seeing, so sketchers must add our ticks to show the cartographer exactly how we are drawing the x-section. In cave both C and D are correct, as Derek says.
It is up to the cartographer to decide how to portray this on a map, and then it falls to common use - we mostly like to see x-section orientated with the the plan tic facing upward. However this is entirely up to the cartographer, and as long as he clearly denotes what he is doing, either way is ok - there is no way to know which way a person will be traveling in the passage. I would expect a cartographer to pick one, and stick with it throughout the cave/map, and I believe the most common it to orient it upwards. However this will probably require the cartographer to reorient some x-sections to reverse them, so that all are oriented the same way.
Remember, with larger maps, we don't always bring the entire map into the cave with us - only copied sections, and these sections may not have north orientation or even the top of the map obvious - this is why I always denote the direction of the cross section on the finished map.

2- I have always taught that the tic near the cross section denotes the (vertical) upward orientation of the cross section. This would seem obvious and extrawork in large passages with details on the floor of the cross section (hard for those rocks to stick to the ceilings). But in uniform tubes with ceiling or floor channels, or in clean vadose passages, the orientation might not always be obvious. We may be able (should be able )to infer it from the plan, but the x-section is an absolute reference to the passage, without resorting to symbols, and may be easier to quickly understand.
I again refer to my example above - especially when giving a section of draft to a sketcher to help them get to a location in a cave, we often print out random areas of maps and then I have folded them in strange ways in cave. These drafts might not have north, or text to help orient the page. It seems an straightforward excersize to me to keep the vertical orientation tics after the cross section so that the caver will automatically orient the cross section upwards and be able to match it to the passage being traveled. (hopefully in the direction it was sketched).

I love discussions like this and can hardly refrain from sticking in my 2cents. However with S&C newsletter not being published regularly, this seems to be a great venue for discussion - We can choose to excerpt these discussions somehow, and create a PDF newlsetter in the near future (Anyone willing to help with this?)

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Re: cross-section technicalities

Postby Extremeophile » Aug 2, 2011 2:06 pm

Thanks for the validation Howard. Your explanation is much clearer than mine and is consistent with my understanding. My own maps have enough ceiling heights, elevations and text that I feel the vertical arrow (i.e. tick next to the cross section) is not needed to properly orient them, but I could imagine this isn't true of every map. Still, the difference in opinion and interpretation of the meaning of these arrows by those contributing to this thread demonstrates how ambiguous they can be... one more reason to leave the vertical arrow off. If I were using offset cross sections with a reference designation, e.g. a and a', then I would probably have a directional arrow on both sides of the passage (as would most cartographers). Clearly some people are interpreting the vertical arrow next to the cross section as another plan view (horizontal plane) orientation arrow, and not a vertical direction arrow.
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Re: cross-section technicalities

Postby ian mckenzie » Aug 2, 2011 6:43 pm

HKalnitz wrote: I have always taught that the tic near the cross section denotes the (vertical) upward orientation of the cross section.


Again, I have never seen that on a cave map. Perhaps I am ill-informed. Can you give us an example of a published survey where the "up" orientation of cross-sections is indicated?
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Re: cross-section technicalities

Postby Dwight Livingston » Aug 2, 2011 6:49 pm

KeyserSoze wrote:Thanks for the replies. I think I've been using the wrong terminology so I'll clarify. It seems like the "tick" mark represents only the horizontal plane, but then there's also the "arrow" that goes with them. I understand the arrow on the plan view represents the direction of view, but what does the arrow on the cross-section side represent?

What started this whole argument was asking which side of the cross section should the rock be on, left-side or right-side? So between example B and D, which one is correct?



D is technically correct, but so not user friendly.
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