🙂
I used a hip chain and an abney to keep track of my actual location... plenty good for recon and planning work. Someone "borrowed" the hip chain years ago but I still use the abney frequently.
This was in rough country where the moss was mare than waist high and the ferns were over my head.
Dietzgen Staff compass> Peter
Not really; we aren't going to run compass line on the entire half mile, just a few short segments and maybe use it as a lightweight sighting device. Most of the traverse is close enough to the line but in a few places it wanders say 50' or so from the line for 2 or 300 feet. This is due to a combination of dead fall, slash piles, brush, foliage and terrain combining to push us off line a little (unless we want to spend a week cutting through all that then the abrupt break in the hill would dictate a couple of short legs if we did).
The alternative is to set up on the stations 50' off and try to get a line point somewhere where the terrain (looking up a steep hill), brush and foliage will allow it.
I'm still in the midst traversing; this is around the NW Corner of the infamous Section 7 (Thompson vs State). We've got the hardest two half miles done. We are ready to dive off another steep hill on the centerline of section going west but the wet season came. This is 2nd growth (maybe 3rd or 4th) Redwood forest in Mendocino County. They don't need it until next spring/summer so we have plenty of time.
We have a winter project down in San Diego County; that will be nice.
Peter
did you ever use what I think they called a Tail Chain? I think it has a scale on one end that you use with the Abney to correct to horizontal out in the field.
Dietzgen Staff compass> Peter
Jud: I seriously doubt that local attraction was the actual cause... I have worked in lots of mineral rich country and "local" was on the scale of several miles. Using the time honored GLO method of running an assumed line, checking the fallings, and then returning on a true line works very well.
I suspect that the users really had no clue about how proper compass traverse work is done... but I work in a bubble like most of us. 😉
David
> did you ever use what I think they called a Tail Chain? I think it has a scale on one end that you use with the Abney to correct to horizontal out in the field.
I don't remember hearing that term... my abney has several interchangeable scales: %, º, etc. I believe one is for slope correction but I never used it... Book of Peter's and Curta is my recalled method.
Dietzgen Staff compass> Peter
I suspect the same thing.
A tool is just a tool.
Heck I made a mess of a piece of wood on the table saw; that doesn't mean the table saw is useless, it just means I did a bad job.
Compass is like the RTK of line oriented equipment. They both seem like magic but they also can lie to you. Your job is to detect the lies.
Peter
I think they are called a trailer tape. I have a 2 chain trailer tape. It has an additional set of graduations (on the back) that begin at 1 ch. and another on the trailer added at 2 ch. They represent the added length for a given vertical angle. So they allow you to lay out a horizontal 1 or 2 chains directly. A little more tricky for intermediate distances I would imagine.
So for example if your first pull is 2 chains at a vertical of 5 degrees, you just go on out to the mark between 5 and 6 and set your pin for 2 chains, and move on.
- jerry
Local Attraction
A couple of points about “local attraction.”
Having spent the better part of the last 35 years working in and around mineral exploration here in North America, and benefiting from the experience of running many miles of geophysical AND Land lines both with “transits” (& Total Stations) AND Compasses (and in some cases coming back and running a Proton Magnetometer over the same lines), I have a little insight into what you MIGHT see in the way of “local attraction.”
Like Peter indicated, many times these anomalies are rather regional in nature, BUT...I have also seen MANY instances where the variation in declination can EXCEED 5-6 DEGREES in as little as 150-200 feet along a “line.” This is enough to really put some wowies in your “line.”
Obviously PROPER field procedures will usually identify these anomalies (in real time) before they become a problem, but even so, there are scenarios where they can really bite you on the rear (non-intervisible [by the compass-man] Stations).
Back in the mid-1980s when I was “setting” hundreds of square miles of 500 foot-(State Plane)-Grid intersections in Nevada, it was “usually” SOP to ALSO get a magnetic bearing observation (back to the Total Station) on EVERY point set. This data was a real eye-opener to the Geologists who were running around doing all sorts of “surveying” with their trusty Bruntons (especially when combined with the results of the Ground-Mag. Survey done by the Geophysicists).
What I am trying to get at, is simply that “local attraction” can be VERY LOCAL, AND of a much greater magnitude than many folks realize.
Loyal
Local Attraction
> What I am trying to get at, is simply that “local attraction” can be VERY LOCAL, AND of a much greater magnitude than many folks realize.
>
> Loyal
I started my career in Nebraska, 1975 and moved to Washington in 1990, so I don't have much experience with a compass.
So I am curious, are these "local attractions" very *strong*? I suppose it would depend on which "local attraction" we are talking about, but, have you ever seen one that would really pull the needle?
Thanks,
Dugger
Local Attraction
Dugger,
In a word...YES!
To the tune of 5-6 DEGREES when moving the compass (either a 4-5 inch staff compass, or a Wild T-0) ONLY 100-200 feet up (or down) the line. Variances in Magnetic Declination can vary a LOT in very short distances when you are around high concentrations of ferro-magnetic materials (especially "veins" of Magnetite and/or Pyrrhotite).
Loyal
Jerry
Wow! great tool! Now that would be a real time saver and save calculation blows too.
great info, thanks
Local Attraction
Great info.
My little bit of compass work has only been on the West coast and Western foothills of the Sierras. I have had no way to either discover or evaluate bends like that.
What parts of the country do you find those kinds of iron ore deposits other than the Great Lakes?
Local Attraction
I found a place up in Sierra County that had at least 5 degrees of local attraction. I had an opportunity to observe a long sight between two stations with my Silva Ranger and it was at least 5 degrees plus. Then I turned around and walked about 600' to a monument and was 50' off when I got there.
I observed geodetic north with a static GPS network.
I have gotten fairly good results with that Silva Ranger, certainly better than that, usually within a degree is possible with care.
Local Attraction
Peter,
The Great Lakes “Iron Belt” is actually an example of a REGIONAL “disturbance” in the “local” magnetic field. This is what I would consider a “long wavelength anomaly.”
What I am talking about, is a very high strength “local” (a “vein” say, that is only a couple of feet across) deposit of Magnetite or Pyrrhotite that has an “Absolute Field Strength Anomaly” in the 10% range (in a [very] local sense)) [sorry]. These kinds of anomalies, I would categorize as being [very] “short wavelength.”
I have seen this kind of phenomena to some degree (or another) from Maine to Alaska. If there is one place that stands out in my [limited] memory, if is a part of the Black Hills in South Dakota. A real stinker...brush, dead-fall, OLD GLO PLSS and Mineral Surveys...
6 DEGREES (absolute) in about 175 feet in places.
I have seen bigger anomalies, but usually spread over much larger areas (let's call then “medium wavelength” anomalies.
There ARE some medium-long wavelength anomalies in the general area you are talking about though (at least that I know about). The “Copper Belt” that runs west of Copperopolis California (in a North-North-West trend), is a prime example of this type of situation.
Magnetic anomalies are kind of like like gold, they is where they is, and unless you are paying attention, you'll miss the prize!
Loyal
Local Attraction
I guess if the original survey was done with a compass in those areas then using a compass would be a good way to follow the Deputy's wandering path.
There is a pair of Record of Survey maps from the 1960s where one LS says he found evidence of the original section corner monument and the other LS said he likes the evidence he found better because he used a compass to follow the footsteps and there was some local attraction. The two are some significant distance apart. I don't remember all the details; they are in Placer County.
Local Attraction
Good for following footsteps, but only if you can deduce where he made his setups. If you do a shorter or longer one than he did, due to trees one of you didn't want to clear, then you could get out of sync with him, get different local attractions, and wander off his path.
Local Attraction
Fascinating! Thanks.
The medium-long wavelength anomalies you speak of I am familiar with, at least in theory. I am astounded to learn of the short wavelength phenomena outside of major deposits.
Thanks again.
What I did was carry the total station back down the line. Set up on traverse points as needed, get a backsight to the prism pole and set some line lath (distances between lath is affected by terrain, brush and where I can see). As soon as we had a segment blazed, flagged and painted we picked up the lath and moved on. I think using the compass would've been almost as much trouble or more trouble than just using the DC and TS to throw out some lath on line. We did this with three people which is me, my employee and the other chief helped us (his employee is on vacation).
Another technique I haven't done is to set lath on a provisional line when you do the initial traverse and station them. Then later move the lath over to the true line by calculating offsets. I didn't do this because we traversed with two people and three tripods so carrying spikes, lath, equipment and clearing line plus laying out traverse was enough to do for one day. Also this would've used up several bundles of lath just for temporary line points. The real permanent line points are the blazed trees; there isn't much reason to leave a bunch of lath out there.
You mean you're running on line? If so, how thick are the trees? In moderately thick timber I can't remember being able to go more than a couple hundred feet without hitting a tree I didn't want to take out. I've done it with a compass with check-in points on each end. When you check in, you go back down (or up) the line and correct the line points proportionately to your error. Maybe you have to be more precise than that. I've haven't done it that way since the olden days.
A little nit-picky point to an old buddy: You refer to your co-worker as your employee. Is that the way your agency categorizes him? I thought that to refer to somebody as your employee, you would hire and/or fire and pay that person.
em·ploy·ee also em·ploy·e (m-ploi, m-, mploi-)
n.
A person who works for another in return for financial or other compensation.
No we traversed along the line but didn't try to stay exactly on line. There are a few spots where we got 50 to 70' off of line but for the most part we managed to stay under 20'. Using traverse points reasonably close to line we were able to get enough lath on line for our purposes. Where we left off Wednesday (had to go do a different task yesterday) is really thick. Our traverse is 10' to 15' off line but we have to clear another line along the boundary. Once we get out of that mess it will be a lot better and we are getting closer to the road so the two of us will handle it next time we get over there. We got what they really need for the Timber Harvest done. Now that we have the traverse in we want to blaze all of the lines because eventually they will need it done.
I'm not sure how to refer to my employee. I am a Supervisor and he is Rank and File. I guess traditionally he would be a chainman or rodman. We also use tripodman. I sign his travel expense claims and timesheets. He is also licensed which is a little unusual to have a Survey Crew with two licensed crew members. Since he is licensed and is in a licensed classification, I have him take on projects where I am working for him. It is a challenge for me to let go of control and I try really hard to not give direction. We could spend all day arguing how to do something so I have to let him do it how he wants to do it. On the other hand it's a little unnerving for him to order his boss around (we are about 20 years apart in age). The crazy thing is his classification pays more than my classification but the job is great so I just live with it the way it is. I could promote into the office and get a raise, no thanks. I could demote and get a raise, naw, I like being the Chief. To paraphrase Mel Brooks, It's Good to be Chief!
Generally our system is he does the front and back halves and I do the instrument (on Forest boundaries). He is young and has the energy and stamina to hike back and forth all day. If we are doing a fire station topo then whoever's project it is does the rod and the other does the instrument.
