DEFINE NORTH

rap, it I use tangential because the direction "north" has only a coincidental relationship to the axis of rotation. The axis of rotation isnt even at true North, and it wobbles and precesses at 2 different periods andfrequencies. Magnetic north is rarely coincidental with the axis or true north , right now it is wandering at a velocity of about 70 km a month. Were due for A FLIP, AT THAT TIME , WHEN magnetic intensity and dec reverses, North "seeking" and South "seeking" will be reversed.
Right now we deal with isogonic lines of declanation that vary so much its better to keep them on the computer rather than in a table in the book of solar ephemeris.

Weve defined North to the exact definition Ive provided. I too like to use optical means and running in benchmarks. Unfortunately , time is money and doing it as an approximation by GPS is good enough.

Brandon, if Ive come across snotty, Im truly sorry. I find your posts really intelligent and so, I was a bit surprised that you pulled the old "Webster" . I put this in science and math , not English so you should have surmised that I wasnt looking for a debate about something I could look up myself in a dictionary.. I can be sometimes snotty , but I really didnt mean to be.In your case, I was being derisive with tongue in cheek, cause youve been in some threads where someone comes up with a dictionary definition as some kind of solid "proof" .
Your answer dwelt more upon the coincidental nature of North to mag north and , axial north. While you were pointing to things that we recognize to be IN A NORTHERN LOCATION , and yet dont provide a definition of North. You could have just as well said "North is where musk oxen are", its true they are, and the axes skewer the earth through the poles, they dont define North,

borg. If we cant measure it we are screwed. We cannot survey on cloudy nights so we can set up GPS with beacon base stations. When we need North, we need it within extremely close tolerances in mining and other endeavors like dam building . 1 degree is 92 ft per mile of error. If I were staking a claim of some of those sections theyve been doing in the Canadian diamond "rush" it would be possible to miss an entire "pipe" in a 100 mile section by as much as 2 miles. Somebody'd get yelled at.

So what is it?

1 degrees okay? 2 degrees? 0.05 degrees?

THEN this thread can get started . . .





PS - magnetic or geographic or celestial or electrical?
What IS the "exact definition Ive provided"? If you could repeat it, it would be useful to me.

psst codeBorg---it's minutes and seconds. Degrees minutes and seconds, and 0.05 degrees is 3 minutes.

Justlike the clock, its Babylonian.

BTW I can see from the red ball on your nose, you've been assimilated.

Rap

Borg-it has to do with your application. For hiking,finding celestial North using a cheap GPS with a WAAS/EGNOS correction channel is plenty good.(The cheapest WAAS enabled Garmin or Magellan system of today is better than any military unit of a few years ago and itll cost you less than 150 bucks) Itll get you to .01% degree . In geoscience and geophysical applications Wekeep searching for a "zero tolerance" survey system. As rap said he would (and so would I) take optical systems from "total stations" and EDM equip if your stepping out by 1/2 mi increments.This is most accurate. Once you locate North either by a "North locating system" or locating polaris for vertical columation in the night, and by vertical elongation in the day (yes we can see polaris in the day by various means)

The stuff in a gps, just to make it almost as accurate as optics is amazing. Like, in order for GPS to work the unit must calculate how long it took for the radio wave (c) to travel from just one satellite to your set.(and it must do this for all satellites its reading so that the unit can calculate its own position wrt to all of them) AND, while its busy calculating that, it makes a calculation that corrects for (c) in the ionosphere and also makes corrections for multipath, where a signal from a satellite is often picked up via it "bouncing" off a roof or a mountain. There are multipath corrections that are made by making an incredible amount of signal calculations and tossing out the spurious ones. Then theres the WAAS/EGNOS post processing which uses a wide area terrain signal. Then on top of that, you have usually up to 22 to 24 satellites available and your Garmin can only pick out 9, so the thing tries to make you happy by choosing the best 9, and by doing so, each time it chooses a different network the finite element grid that defines the GPS network in relation to space(cuz the satellites are busy trying to figure out where the hell they are in space). Theres a lot of calculating going on, thats why a gps usually takes a few moments to make sure before it pumps out your location and then draws you a compass rose. Now the surveying GPS stations are waay more complicated than that, they make random position calculations and use multiple "swing" calculations for the angle of the ionospheric correction and they also are busy radioing to at least 2 other GPS stations that are parked on known USGS and USCG benchmarks and add another set of calculations.
Whats youre need?

North is by definition the vertical columation of Polaris Delta and Mizar (which sitsunder and is occulted by Alcor).In the daytime it is the vertical "elongation" of polaris. This is the old fashioned way but still the working definition since all other concepts (Mag north, polar north, axial trace) are based upon this. There is a fascinating story in Comptons old "Field Geology" of how this was established and how ephemeris tables and the secondary optical methods were developed, and how a magnetic "zero" line was established and how declination corrections were set up.
As our technology advances, the bases upon which these technologies depend are more and more forgotten.Ive had a student return and tell me that they used old fashioned NOrth in a survey in Russia because their total station blew and they couldnt fix it but the Russians had an optical plummet transit system, which saved their asses in an oil field

If the magnetic poles shift suddenly there is a well defended hypothesis that the EMP from the magnetic might fry every piece of technology beyond tubes and relays. No cell phones, no GPS, no computers. Transportation won't fare much better, all those electronic systems and all. Could be the only motors running will be a lawnmower with points, with communication by hard wire and hand signals.

Curious that the gyroscopic precision (or is it percussion?) is that big. I knew the wobble was on a 22,000 year circuit but I had no idea that precision is that great.

As for pipelines,damns, and mines, in a long long ago life I surveyed airports and pieces of the Ohio River.

As for finding North then, that was the days of finding the benchmarks and working from there. But I can remember one shot of the Ohio River that was so long it had three QA required setups. In these days of GPS to a cm in a mile, are surveys even necessary? All you need are the endpoint coordinates and a profile. The surveying is done by the software (saying this TIC).

Rap
Rap

rap. Ive flown into Nigeria where there were no benchmarks , just aerial photos and a total EDM. Wed locate N, survey and plot our data. Then survey our way out to a town . Talk about QA. Wed have to have crews resurveying over and over to develop a closure error function.
The poles are shifting now. They are starting by an increase in the velocity of the wandering of the North pole and the decline in the total field at the poles . This is being offset somewhat by an "appearance" of a pseudo pole in the Pacific. AGU has articles periodically. The predicted decline of the total field to zero , as Ive been told, is about 1000 to 10000 years. This could be a cause for some environmental adaptations as melanomas rise .
Im speculating here but I think that very hairy guys will be favored in such a high solar radiation world.

Oh, okay. :-)

Multipath ... ionosphere ... Wide Area Augmentation System . . .
omigod I think I just oh oh yes I it's they the numbers I'm . . .
did you happen to see the gyroscope I mentioned two times already?

Unbelievable!

For fifty bucks, fifty puny little measely tiny insignificant statistically
and financially unremuneratively inconsequential bucks ... you can get a
"Garmin GPS III+ including manual, case, cigar-lighter power and antenna extension."
It says so right here in my Boonytown Mountain Classifieds. Fifty bucks!

Interferometry. You know how holograms create a tiny interference pattern
when the subject is moved by even a nanometer?? The radio waves from multiple GPS
satellites create clear wave interference when one wavelength is shifted against
another from a different satellite. Precision baby, and LOTS of it! Miniscule
frequency shifting gives us accuracy, so it's not just time and atomic clocks
and synchronizing your azimuth readings but frequency measurement granulated
against the calibrated wavelengths of 24 damn satellite tranmissions simultaneously.

Booya.

'Course, farmerman never answered my question . . . but who cares?!?

I'm late in finding this forum, but my North would be determined by the use of our sun and a sextent.

Edit: BTW, I posted this answer after reading part of the first page.

How the Vikings did it:

"... the sun indicates not only east (at sunrise) and west (at sunset), but at noon the sun is due south, and in the months when the sun does not set below the horizon, the position of the sun at midnight indicates due north."

Forgive my ignorance, but I'm curious about viable alternatives.

Is the orbit of the moon stable enough to be used to calculate true north given you know the date and time? You could sometimes use it by day (but sometimes not at night)

DEFINE NORTH: The direction one travels in the United States when searching for humorless sex and bland food.

borg, I wasnt ignoring your gyroscope thingy. When I looked at it I saw that it was a gyroscope with a total station . The gyroscope doesnt FIND north , it carries it from the original base station. The total station is actually an Electronic Distance Measuring laser. I believe that this system locates N and gyroscopic precession allows minor deflections in the gyroscope spin to be calculated from place to place.

I always had the notion when I was little that North was anywhere in front of me.

I think that's half the picture maybe... No base station is actually needed.

If you take any gyroscope that is not yet spinning,
start it going, and just let it spin freely with no forces to push it
then there is no precession to it at all.

Simply watch the gyroscope as it keeps to it's position.
After twelve hours the earth will have rotated halfway around it, so that it
will be facing the opposite direction, 180-degrees from where it started.

In six hours the gyro "appears" to shift 90 degrees.
In six minutes, the gyro appears to shift 1.5 degrees.

So, to find the exact direction the earth is rotating, simply watch the
gyroscope gradually tilt 1 degree every four minutes.

That's why the advertisement says it takes the device 20 minutes to determine True North.
It's waiting for the Earth to turn 5 degrees, so the axis of that turn can be observed.

You don't need to measure the distance to anything, or move
from place to place, or have ANY external reference at all.




PS - This is completely unrelated to the magnetic North that a compass measures. That has nothing at all to do with geographic North. It also has nothing to do with solar North or galactic North, which can also be observed.

PPS - Do you happen to know if (and how) a GPS system can determine North?

Ok Ill take that as something Ill have to look into. Weve never used gyros except to carry points. Why do they have the total station EDM attached? That is a surveying instrument, thats why I guessed that the total station "found" north and the gyro allowed it to be moved. Do you have experience with these?

GPS operates like a finite element grid in a polar coordinate system. North is determined by elongation of polaris via the satellites. Ive been told that the network operates as a single organism and determines north. Each satellite then sends its component of the equation to the receievers. There are a number of really new algorithms built into newer and newer gps so that all those issues of spurious signals and scatter get whipped out and youre left with the answer. Ive tried to show that it works by keeping a GPS northing arrow next to an alidade. The difference of the two directions is the compass declination from polaris to magnetic.

In essence the sat network IS an interferometer except in reverse.

But isn't the magnetic changing?

constantly

"Do you happen to know if (and how) a GPS system can determine North?"





. . . I'll have to think about it some more.

As stated, I think it's only physically possible with a directional antenna
(usu. a parabolic dish or a rod, with larger ones more accurate),
or by taking readings from two or more different places.

If a handheld GPS has a small "point" antenna, then it would
receive exactly the same input signal no matter which way you spin it.