How do I determine Clino error?

[jlillest]

Mostly you are time ahead by taking the backsights instead of conjuring voodoo on data reduction. Especially since you think that this cave may tie in to other caves at some point.

You guys can spend your weekends how you wish, but you're not going to convince me that backsights are going to save me any time.

In lieu of setting up a complex course and pulling out the garden hose (so that it can freeze overnight), I picked a couple of distant points and found a clino error of +2 using Derek's helpful explanation. I verified this with a second instrument reader. This works well with the data as it comes close to fitting the estimated 2 degree gradient of the stream.

...I'll just add that you can do back sights with a single set of instruments

I'm fully aware of the backsighting process, no need to explain. (Though thanks for providing options for those that may not have known)

...and since the sketch is nearly always the rate limiting factor in any survey, it doesn't take any more time.

Egad! You need some faster sketchers. I believe slow sketching to be one of the biggest detriments to survey team morale. Low morale + cold caves = fatigued instrument readers. Fatigued instrument readers make blunders, and when you have the pressure of fs/bs agreement with a clino that has an internal error of +2, well you do the math. Different strokes for different folks, but if your sketcher takes longer than two instrument readers reading fs/bs, then you've got some other problems.

Besides, for the caves in question we know the caves connect because of multiple positive dye-traces, but it'll be hard to collect a super-accurate data set when the middle half-mile of passage can only be mapped using a Grade 2 survey.

-Jon

[John Lovaas]

I did a little experimentation with my Suunto Tandem and Sisteco Surveymaster. I couldn't get the clinos on either to budge with either my Sten light or a very strong hand-held magnet. I would say that the myth I heard about clinos being affected by iron or magnets is definitely busted.

Hi Derek-

I know there was one Brunton clino at Hamilton Valley that would deflect if a light was brought near- I saw it with my own eyes.

That being said, I think it was probably an isolated issue- I'd wager that whoever manufactured the Brunton's moving part/s switched stainless steel or aluminum with carbon steel- or their stainless supplier messed up somehow.

[Extremeophile]

Hmmm. I'm still not sure this makes sense. If you were surveying upstream, and the data reduction shows the end of your survey being below the beginning, then I would expect something like a -2 degree offset, not the other way round.

[Chads93GT]

...and since the sketch is nearly always the rate limiting factor in any survey, it doesn't take any more time.

Egad! You need some faster sketchers. I believe slow sketching to be one of the biggest detriments to survey team morale. Low morale + cold caves = fatigued instrument readers. Fatigued instrument readers make blunders, and when you have the pressure of fs/bs agreement with a clino that has an internal error of +2, well you do the math. Different strokes for different folks, but if your sketcher takes longer than two instrument readers reading fs/bs, then you've got some other problems.

Besides, for the caves in question we know the caves connect because of multiple positive dye-traces, but it'll be hard to collect a super-accurate data set when the middle half-mile of passage can only be mapped using a Grade 2 survey.

-Jon

Since you are making assumptions that sketchers are slow if they take time sketching, I am going t make the assumption that you dont have any detail in yoru sketching or you are surveying very simple cave passages. When you sketch river caves, with loads of ceiling ledges, flowstones, bridges, multiple levels stacked on top of each other and profiles that resemble the letter S, or large breakdown areas, you will find your sketching to be slower. That is of course unless all you are doing is drawing walls, no profiles, and just writing the words (breakdown) instead of drawing significantly large boulders to scale. Some people actually want their maps to look like the cave.

Then again.....I am only assuming of course.

Its like the guys around here who brag that back in the day they could survey 2000-3000 feet a day. then you look at the maps produced and its nothing more than a line plot with walls. Yeah, great mapping there.

[John Lovaas]

Different strokes for different folks, but if your sketcher takes longer than two instrument readers reading fs/bs, then you've got some other problems.

Kind of a quantum paradox- even if your crew isn't doing backsights, wouldn't your sketcher have to wait for the distance/azimuth/vertical before drawing anything, yes? I mean, the only way a sketcher could be be faster than the instrument readers is if the sketcher is working solo, I guess?

[jlillest]

Hmmm. I'm still not sure this makes sense. If you were surveying upstream, and the data reduction shows the end of your survey being below the beginning, then I would expect something like a -2 degree offset, not the other way round.

OK, not enough time spent in typing up my response. You're correct, the error is -2, so I added a correction of +2. I explained it backwards.

[George Dasher]

Sorry I found this post soooo late.

Shoot to some point (with your clinometer) that has a zero inclination.

Then flip the instrument over so that you are reading the back of the dial. The big viewing window should now be to your right, instead of your left.

The back of the dial should be blank, except for one mark. That is a zero mark.

Shoot to the same point, using that mark. That "backside" zero mark should line up on your point--if your clinometer is accurate.

If your instrument is not accurate, then compare the zero indicated by the "backside mark" to the proper reading obtained by reading the "front side" of your clinometer. The difference is twice the error your instrument is producing with each reading.

But, to be honest, your problem (of reading uphill shots in a downstream passage (or the other way around)) is not unknown. You're just going to have to do some simple math, once you know the ends of your survey to correct it.

But check your inclinometer first. Especially since it is such a simple check.

Now the bad news: some clinometers don't have this zero mark on the back of their dial. In which case you have to use a compass course.

[jlillest]

Thanks George.

[Bob Thrun]

The procedure that George Dasher gave, using the backside mark on some Suuntos, saves a little walking, but you do not need the backside mark to determine a clinometer bias. All you need to do is take a very solid foresight and backsight between the same pair of points and compare them. just read as carefully and with as much procision as you can.

The backside mark can be used to tell if the pivot is offcenter relative to the markings on the dial.

[HKalnitz]

I have a quick test I have done to check my clinos - even once in a cave:
Find a nice smooth surface - it does not need to be level, just locally flat. I have used countertops, table saw tops, clipboards on rocks, at work I have a granite measuring surface.
Place your clino on it on edge and (without touching it) take the reading.
Pivot it 180 degrees around the center of the body (different locations depending on whether it is a tandam, a survey master, or an individual clino), so that you are shooting in the opposite direction
Read again. Because you are actually remeasuring the same slope in the opposite direction , you should get the opposite reading. no need to walk back and forth, and much less possibility of readng errors.

This is a quick way to see if there is a clino issue. I have turned up units where the clino is loose in the body so that card has rotated, giving me incorrect readings - I still believe this to be one of the most prevalent issues, especially in older surveymasters (used to be sisteco, now owned by brunton)

Howard

[Extremeophile]

I like that a lot better Howard - much quicker. I suspect you can't do it with a Tandem though due to the odd shape.

I spend much time while running or taking a shower thinking about ways to make surveying more efficient. Doesn't everyone?

I put together a timeline in table format. This example is for a 3 person team using 2 sets of instruments (as is commonly done in the Black Hills and CO). I've been working on a table for other scenarios - e.g. 4 person team, 1 set of instruments, etc. I think by knowing your role, and working in the most efficient order, survey shots can be completed in roughly 6 min - that comes to 10 shots per hour, which most would agree is pretty good. If you're doing running profiles it would slow things down a bit.

[Squirrel Girl]

Egad! You need some faster sketchers. I believe slow sketching to be one of the biggest detriments to survey team morale. Low morale + cold caves = fatigued instrument readers. Fatigued instrument readers make blunders, and when you have the pressure of fs/bs agreement with a clino that has an internal error of +2, well you do the math. Different strokes for different folks, but if your sketcher takes longer than two instrument readers reading fs/bs, then you've got some other problems.

Hah, hah, hah, hah! I guess that means you'll never let me sketch for you, huh?? It all depends on the complexity of the cave. If it's not too bad, I imagine I can do it faster than your limit. But I'm not too fast.

On the other hand, Give me a half hour, send me into an U/W cave where I have to do *all* the readings *and* sketch--and you get a lousy 5 stations done. BTW, without knots, I estimated the first shot three times and got the following lengths: 35', 45', and 62'. When we go back to mop up those jumps, everyone should be required to estimate that first shot and we can average the results!

[Bob Thrun]

I put together a timeline in table format. This example is for a 3 person team using 2 sets of instruments (as is commonly done in the Black Hills and CO).

I notice that half the time in the timeline is spent by the point man scouting the route and selecting a survey station. This might be the case in a breakdown pile, but in most caves the time to find a new station is the time it takes to walk there.

I like to have the tape left on the floor so I can walk along it to determine the locations of details as I sketch.

[Extremeophile]

I put together a timeline in table format. This example is for a 3 person team using 2 sets of instruments (as is commonly done in the Black Hills and CO).

I notice that half the time in the timeline is spent by the point man scouting the route and selecting a survey station. This might be the case in a breakdown pile, but in most caves the time to find a new station is the time it takes to walk there.

I like to have the tape left on the floor so I can walk along it to determine the locations of details as I sketch.

I, like most surveyors, find the sketch to be the rate limiting step. So if locating the next station is simple and inventory is not being collected, then naturally there will be some slack time for some members of the party. To borrow from the time managment world... there's a critical path (i.e. the sequence of activities that takes the most time), and the focus of the team should be to reduce that time.

I've been using a LASER rangefinder a lot for distance measurements, and it has it's advantages and disadvantages. The big disadvantage is the inability to leave the tape in place while sketching for reference. I often take a second rangefinder that I just use for sketching, but it's not the same.

[brad81286]

You know Jon, you really need to jump on this backsight bandwagon. I too was once a foresight man, but after listening to all these backsight rants, I decided to dump the foresight's for the backsight's. I really don't know what you have against it- it takes me the exact same amount of time.

See you Friday,

-Brad