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YeOleImposter

Datasheet - info that can be ignored?

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I am trying to pare down the info that I keep on my palm for each benchmark -

 

One item that I am considering stripping are the Magnetic & Stability lines ie:

MAGNETIC: N = NO MAGNETIC MATERIAL

STABILITY: C = MAY HOLD, BUT OF TYPE COMMONLY SUBJECT TO

STABILITY: SURFACE MOTION

 

Any reason to keep these? Seems that for the most part they are always the same? Maybe not in other parts of the country?

 

Thanks

Gary

 

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The magnetic and stability references to the benchmarks is generally information for surveyors. The reference to the magnetics of, or within, a benchmark is to help the mark be located with a metal detector. Often times a mark is made of only concrete and a brass cap. Some of the newer marks are in an aluminum cover. None of these materials are detectable with the type of magnetic locator is used by surveyors. Sometimes, however, a magnet will be placed on, or near the mark so they can be detected. This is very helpful if it is an underground mark. For the type of benchmark hunting we're doing here (on Geocaching.com), it is fairly irrelevant information unless you are using a metal detector too.

 

Surveyors use the stability reference to help them determine whether or not they want to use a particular mark. A mark set in an area with higher stability is going to be a better mark to use since it has a less likely chance of having moved since the elevation for it was determined. This is also is fairly irrelevant information for the type of benchmark hunting we're doing here.

 

Keep on Caching! (and Benchmarking!)

- Kewaneh

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quote:
MAGNETIC: N = NO MAGNETIC MATERIAL


Is this of use even if we are using a "normal" metal detector and not a "magnetic" detector? I thought I read that the brass cap would show up well. Not sure about an aluminum one. That could be a problem.

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Assuming that your definition of a 'normal' metal detector is one similar to what a treasure hunter might use at a city park, you may be able to pick up some other types of metal other than iron. Treasure hunters commonly search for and detect gold and silver as well as aluminum and brass. If you use this type of metal detector in your benchmark searches, they may be able to find that buried mark.

 

The metal/magnetic detectors that are used by surveyors generally do not pick up non-ferrous metals. (Ferrous metals are generally metals that rust and that magnets are attracted to; the most common is iron.) The detectors are designed to pick up electro-magnetic fields that come from ferrous metals, magnets, and live electrical wires. They cannot 'see' brass or aluminum which is why some surveyors, when they set a benchmark that is constructed from non-magnetic materials, will place a magnet near the mark. (Big Fat Disclaimer: I am neither an electrical engineer or a geologist. This is just my understanding of how the metal/magnetic detectors that surveyors use work.)

 

Keep on Caching! (and Benchmarking!)

- Kewaneh

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quote:
Originally posted by Kewaneh & Shark:

Assuming that your definition of a 'normal' metal detector is one similar to what a treasure hunter might use at a city park, you may be able to pick up some other types of metal other than iron. Treasure hunters commonly search for and detect gold and silver as well as aluminum and brass. If you use this type of metal detector in your benchmark searches, they may be able to find that buried mark.


I'm talking about the kind you find in RadioShack. Say $60 or so.

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Type many professionals use

 

Very expensive (start at $860) but also very good.

 

btw

Another reason for knowing if the mark has any magnetic materials is for certain other survey operations like "Gravity Surveys" and mineral exploration and you can avoid using that mark if your equipment or results can be so influenced.

 

Mike

Survey Tech (Retired)

 

[This message was edited by elcamino on October 14, 2003 at 05:27 AM.]

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I would imagine that a less expensive metal detector similar to the types sold at Radio Shack or other hobby stores could help you in your benchmark searches. You may have to check on each model to see just what it can actually 'find'. I personally have no experience with the hobby-type metal detectors. I do have experience with the Schonstedt brand of survey grade detectors. (I have a Schonstedt model GA-52Cx in my survey truck.) ElCamino provided a link to their website in his above post.

 

Keep on Caching! (and Benchmarking!)

- Kewaneh

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Getting back to the title of this thread, maybe a better question is what should one KEEP from the datasheet. To give a little background on this - YeOleImposter and I were discussing CacheMate and Benchmarking. I mentioned that I trim down the datasheets prior to running BMGPX. Because the end results go into a Palm Pilot with a finite amount of memory and a screen display small enough that I don’t want to constantly scroll to get to the “meat” of the datasheet, this is what I do:

 

  • I keep all the lines from the top of the datasheet until the first blank line. This gives the title and whatnot.

  • I keep the line that starts with “* NAD” since this gives the mark’s horizontal location.

  • I keep the lines starting with a underscore except for “STABILITY” and “SPATIAL ADDRESS”.

  • I keep the lines starting with “History” as it gives a good summary

  • I keep all lines starting with a single quote – however I do shift everything to lower case to make it more readable.

 

So in short I discard everything about the mark’s vertical location, adjustments and Superceded Survey Control. I don’t see those being useful to someone simply trying to find the mark. (But I’m willing to be educated if I’m wrong.)

 

The actual process is a bit more complex then I’ve outlined to deal with blank lines and headers, but it gives the general idea of what I keep and what I toss. I also add a “NNNN” at the end of the datasheet. If I see that in CacheMate, I know that the whole datasheet made it though the CM’s 8K limit.

 

The result of this trimming is my county DAT file went from 4.29MB to 2.26MB. The GPX reduction is less impressive – I think about 30%.

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I think the best rule of thumb would be that if you don't find it useful, don't include it in your file. I would imagine that most of us get different information off of the datasheets than others.

 

Keep on Caching! (and Benchmarking!)

- Kewaneh

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