Deviation question on 1994 survey map

The best way to adjust a compass locally is to observe a known line and make the compass match that line. For example I used to use a compass often, outside our office at the time was a street that had a bearing of S45dE, N45dW, I would stand on the curb line, sight down it and slide my compass adjustment till I got the correct angle, cross the street and check it.?ÿ

For your survey, look down one of your lines and adjust to the record, if you can't see on line then possibly an offset line. You want to do it both directions as a check and to overcome any local attraction. If you can't do that do a north-south or east-west street in the area.?ÿ

The lines in wooded areas were usually cut at least partly and they may have been blazed when the survey was done. I would look for that evidence to begin with.?ÿ

I think you might be seeing that surveying the 7.5 acres isn't a simple task.

I have been involved with tree appraisals and the value of some are shocking. I would be very careful cutting down anything until I was really sure.?ÿ Cut a few trees on the wrong side of line and get sent a bill for tens of thousands of dollars.

It doesn't take much to see if it was magnetic, 15 degrees will show up as an eyeball shift from due north, if you need to know where north is look for Polaris.?ÿ

@mightymoe, I like that answer.

If need be, go to hardware store, buy 2 sticks of 2" dia electrical pvc conduit. And 2 steel fence posts. Drive the posts right near the rebar you found, and put the pvc pipe over them. Paint the end with bright paint.

Use these to sight in your line.

2.) Go to hardware store. Buy paint, and a bundle of 4' lath or tomatoe stakes. And a 100' cloth tape.

For this example, the plat says one line is 1000' long.

Start at a known rebar. Set stake over rebar. Guess your line. Measure 100', set painted stake. Eye-balling those 2 stakes, go another 100'. Repeat. Until you are at 1000'. You missed it by 100'. You now have a direct ratio.

1000 to 100.

Move your first stake at 100' from corner 10 feet. Move your second stake 20 feet. And so forth. Read your compass on this line of stakes. Whatever it reads, subtract it from the bearing shown on plat. This is your declination.

Apply this declination to all bearings shown on plat. Remember to think in terms of clockwise, or counterclockwise.?ÿ

"Look ma, I'm a surveyor"!

They used to teach this stuff in school.

Enjoy.

N

Another way, go buy 2 fancy real bright flashlights. Find 2 consecutive monuments. Go out at dusk, and have one helper stand over the found monument, and shine it at you, while you are on the other one. Now, have a 3rd person set tomatoes stake on line.

None of this friendly, do it yourself advice will help you, if you use the wrong corner markers.

Enjoy!

N

Posted by: @lou-adams

Not being a spring chicken, it sometime appears to me that I get a different reading every time I put the compass up to the eye, depending on weather I close one eye or the other, or use both

There is a name for this. But I'm old, and can't remember it.

For this problem, close one eye, and only use your chosen eye, start to finish. Sight over the top of the compass.?ÿ

N

"There is a name for this. But I'm old, and can't remember it"

Parallax

I advised a young fellow once to measure an offset from the true line that would clear all obstructions to the line of sight from end to end.?ÿ Then empty his deer rifle of all ammunition.?ÿ Set up over the offset point on one end and aim at the other offset point.?ÿ Then have someone place flags/stakes at appropriate locations along that line while chatting on their cell phones or using walkie talkies.

PLEASE NOTE:?ÿ THE RIFLE MUST CONTAIN NO AMMUNITION WHILE BEING USED.

No one has addressed my questions about deviation.?ÿ ?ÿShould I assume that everyone agrees that since there is nothing like what is shown here... https://www.usgs.gov/faqs/what-do-different-north-arrows-a-usgs-topographic-map-mean?qt-news_science_products=0#qt-news_science_products, and because the arrow on my survey looks a lot like the middlemagnetic arrow on this page... http://www.cavesurvey.com/North%20Arrows.HTM, that they used magnetic north with no deviation included?

And thus, I should be subtracting 1.47 from every degree line?

Published deviation values are only one component of the whole adjustment of rotational values.

It could get very wordy, to explain all the speculative ins and outs of this subject.

Buy 50 compasses, make a nice bracket, from non magnetic material, set it all up, and they will all read a little different from each other.

Take one compass, and throw it in your shirt pocket. Work on the stereo in your '57 t-bird, or '69 Camaro, and you can change the declination in that compass by 1, or 2 degrees, by the big magnets in the speakers, being in close proximity. Go back to surveying. Now that compass is a bit different. You would have to also know at what point the compass was exposed to the magnets. Or, bending over the ignition coil.?ÿ

Or, one guy on the crew had a compass in his pocket already, and carried the one used on this job in the same pocket....

We typically don't use compasses to determine directions, except for short distances, like witness trees.

Determining deviation for an area, and what happened on a survey don't typically have a direct relationship.

So, go find 2 genuine points on this survey, that are intervisable, and determine the algebraic difference between your compass, and your survey. It usually will not vary a lot, but if you had every point on this survey found, and intervisable, and shot every line, from both ends, you would now see up a degree of variation (usually) on the SAME line, from both ends. Magnetic deviation is a constantly changing variable, unless you mitigate all the sources of change, and still magnetism in the ground can affect it.

You have day-dreamed the deviation value to be "an absolute", when it is a bit rougher than your assumption. It is just more efficient to work with observed local values.

Our old field books have hundreds of entries: 356-1/4 SC#2

That means an azimuth of 356 and a quarter on suunto compass number two. We then inverse the coords, and find N 1 E. We now subtract these algebraicly, 4-3/4 degrees is the declination for suunto number two. We also have compared SC #2, and #4, (another crew member is carrying #4), and we already know by comparing that #4 reads more clockwise by 1-1/4 degrees. So 4-3/4 degrees minus 1-1/4 degrees. So, it's declination is 3-1/2 degrees.?ÿ

It's "all in a day's work", but there is no substitute for IN THE DIRT direct observations. Declination can vary from job to job, by 1, 2,?ÿ or more degrees. And, you are trying to read more value into govt. Published numbers than we read into them.

Happy Surveying!

N

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I think you have the theory right, but I worry that it really wasn't a magnetic compass survey.

In 1994 in most areas, the actual measurements were being done with a transit or total station as angles taken at the corners, not compass measurements, and then converted to bearings on the plat.?ÿ

One bearing was used to orient the whole survey, and you don't know where that bearing came from.?ÿ It might not be a real magnetic compass measurement.?ÿ It is common practice to start with one line assumed to have the bearing given on an adjoining survey, whose date and compass accuracy, or other basis of bearings, is unknown to the surveyor doing the present parcel.

That is why the advice about finding one line to work from makes a lot of sense, and what most surveyors would try to do.

If it is magnetic it's probably based historical local lands that the surveyor is retracing.

In a colonial state that bearing might originate in the 1600's.

For now forget about the NGS calculator.?ÿ

Match your compass to the property lines, that's how it's done.?ÿ

And if it's actually rotated from true north 15d then it should be seen visually.?ÿ

Look at your GIS, there should be a tool to inverse along lines. The GIS is probably rotated to state plane, you can get the bearing along your line and see if it matches the survey. 15d will leap out.?ÿ

post your survey map, there may be a notation on it that explains the basis of bearings.?ÿ

Google Earth 4/27/2016 seems to show stone walls that would mark parts of the boundary. Look along your parcel's east side from the main road northerly to a bend going east.?ÿ That seems to match the tax map shape for what I think is your parcel (7-sided).?ÿ The tax map I found isn't nearly as detailed as the ones around here, so I can't do much more with it.

That long wall would be an excellent place to find a compass declination to match the survey.

That wall is about 11 or 11 1/2 degrees west of north in Google Earth coordinates. Not sure if that is geodetic, UTM, SPC, or what.

I would say it's a geodetic direction from Google Earth, the two long walls, or fences visible are easy enough to see, there is a 125' jog east west. It looks like after going northerly from the main road it angles southeast then turns east at a N82dE bearing then heads northerly at about N20dW. If that fits the bearings recorded on the survey then the survey isn't magnetic.?ÿ

Bill93 and MightMoe

What is going on here, you guys FBI or Interpol (I gave those jewels back!)??ÿ Ahh, I get it.?ÿ When I mentioned the Lat and Long on the NCEI site, that pointed you to my property.?ÿ

You are correct, on the back of the property (away from the street North end), there are rods at each end, and on the SE side there is a stone wall.?ÿ Where that wall stops and heads nw and and then ends there is a drill hole.?ÿ It is from that drill hole to the street (519 ft to the ulility pole, that I do not have a clear line (trees)).?ÿ The property lines do not follow the stone wall (from the drill point) that you might see heading down.?ÿ On the left side side line, going to the street from the rear, I found a drill hole at the end of the rock wall that continues from that right side property line?ÿ (breaks in the middle for driveway in).?ÿ It must have been a long time ago that these holes were drilled, this hole is in a flat rock that appears to be the end of the wall, that is over a water path (sometime water, sometimes not), and in between some trees that are a couple of feet wide (largetallpartially rotted), if is off kilter because it touches the trees roots on both ends, so it is not exactly clear where it was origionally.?ÿ There is no clear line to it from the rear of the property (347 ft to that drill point), and again no clear line from that drill point to the street (488 ft).?ÿ On the street, at that point, the survey indicates "conc bnd fnd"...I will be darned if I can find it.?ÿ The street goes up hill from the right side line (at the pole), and while I have tried to measure as pricesly as I can considering going uphill, and sticking a rod in the ground, I cannot find it.?ÿ How bigwide would it be.?ÿ It should be pretty much in line with the second utility pole.?ÿ If I could find that marker, it would help me with determining the lines on that side.?ÿ Anyway, that is what I am trying to determine preicesly (as much as possibly, but possibly not possible because of other comments made here).

Without going into a lot of details (because I really am trying to clean the lot and determine my lot lines, and that is past history), origionally I thought that I was purchasing more acres (Surprise, surprise, it was less).?ÿ Anyway, since then, being a computer type, I wrote a program for the phone (Android only right now), that can take the lot line information (metes and bounds), and calculate acreage and draw the lines.?ÿ If the program had existed when I bought the property, there would have been no questions as to what the acreage really was (I have no regrets about the purchase).?ÿ Problem is it is only for straight lines.?ÿ My understanding is that there is no standard way of calculating curves, and thus no why to know what method the surveyor used (at least, that is what I was told), so, I have not bothered to polish and market this program. It does not use the internet, all is done on the phone, and obviously can be emailed also.

I started on the left side lower line, and end up on the bottom (street).?ÿ I did not start this posting with the idea of asking what you guys think about the benefits of a program that can do this (from a property buyers prespective), or if there is a standard way of calculating curves (I really am trying to pinpoint my lines), but since you know where I am now, what the heck.?ÿ Or, should this be a different posting (if it can be posted at all on this forum).

?ÿ

Finding that "Conc bnd fnd", would definity help.

Knowing declination tells us nothing, without a knowledge of WHAT THAT SURVEY WAS BASED ON, in a rotational sense.

We have hundreds of surveys out there, that are based on magnetic north. How this was done was set up transit on random nail. Backsite another random nail. Measure magnetic to this line, and add azimuth 2, or 3 degrees. That was it. No more. From then on, we turned angles, all from that assumed 2 or 3 degree declination shot at the very first traverse point. This made most surveys within 1 to 2 degrees rotationally of each other. But, that was all. Another surveyor would do the same, but not correct. So, his surveys were on magnetic. 2 of his surveys, both on magnetic bearings, could differ by 1-3 degrees of each other.

I'm saying we don't know the rotation of your survey, as it relates to somebody's magnetic compass. Or, your suunto.

I know it's not what you wanted to hear, but hey, that new truck price failed to thrill me too!

In linear measurement, think about surveying with your wife's car odometer. To the closest tenth of a mile. That's 528 feet. And complaining because you missed by 50 feet. A compass is only a rough tool. Unless calibrated to a given system. Calibration can "make it read to the hundredth of a mile". Well, that's 52.8 feet. That's better, but it's still a rough tool. It with careful calibration, can be accurate to 1/4 degree, or 1/2 degree.

Tangent of 1/2 degree, in 1000 feet, is 8.7 feet. That makes it useful. But not overly accurate.

The publishing of declination via the govt, has given you an impression of certainty, and accuracy, that quite simply does not exist.

Those published values are handy for airplanes, and other things. But it deteriorated in close proximity to the ground. You can shoot the same line, from both ends, with 1/2 to 1 degree difference magnetic, and it's not going to raise an eyebrow to a person experienced with these tools.

Have fun!

N