True North or Magnetic North ??

[HMF4]

Which one do should you use??

[+leatherman]

If your asking in regards to a GPSr, it doesn't matter. The GPSr recieves signals from SPACE

The coordinates will be the same wheather you use magnetic or not.

If your asking about a digital compass feature. I don't think it really matters. Their pretty inaccurate anyways.

 

Preparation, the first law to survival.

[+unclerojelio]

quote:

---

Originally posted by HMF4:

Which one do should you use??

---

 

Depends on what you are trying to do.

 

... Two roads diverged in a wood, and I--

I took the one less traveled by, ...

 

unclerojelio

[Tahosa and Sons]

Now what North am I talking about. There are 3 of them.

 

Put your GPS to Mag, so it talks to your compass.

Understand declination or get an adjutable compass.

 

The "Bushwhacker"

Exitus acta probat

>>--->

[Tahosa and Sons]

Now what North am I talking about. There are 3 of them.

 

Put your GPS to Mag, so it talks to your compass.

Understand declination or get an adjutable compass.

 

The "Bushwhacker"

Exitus acta probat

>>--->

[HMF4]

I should really do some research before posting stuff.

 

I'm pretty new to this (only 8 caches found) and just started using a compass when finding caches.

 

Since I'm not using a map of any kind, I think I'll set the GPS to mag north and be done with it.

 

If I ever start using topo maps I'll have to get "smart" about declination. As near as I can tell I should be at less than a degree east here in SE Wisconsin - so it shouldn't be to big a deal.

 

Thanks!!!

[+apersson850]

You can check the declination with the GPS, or at least I can with my Vista. I don't know if that's possible with all models.

 

Just go to the set-up/course screen, then select magnetic north. It will show you the declination, for your current position.

 

If you want to know the declination value somewhere else, do this too:

 

Turn GPS off.

Select New location at the sat screen, then go for the map option.

Pan the map to wherever you want, then press Enter (the click stick).

 

Go back to the course setting screen, and check what the declination is now.

 

All this is of course dependent on the tables stored in the firmware of the GPS, but will all these updates coming out all the time, the manufacturers have a lot of opportunities to upgrade the tables with new data. Maybe they don't, but at least they have many chances.

 

Anders

[+GEO*Trailblazer 1]

THIS COULD GO INTO A LENGTHY DISCUSSION. Refer to the Isogonic Chart, or the annual westward slippage. In the 1840's _+ the magnetic declination was observered as being 8 degrees in our area, original BLM Surveys, current observations are at 0_+ declination thus the magnetic field has moved approx. 7.5_+ degrees. this has to do with a therory scientists,and I are working on now, called EXPANTION of the UNIVERSE or the BIG BANG THEORY. from many observations and scientific studies they use to theorize the magnetic field acted like a pedilum reaching the 0 mark approx. every 150 years then to max. to 0 then to min. But the GPS True north is grid north, and in our area the diffrence is 4 degrees when you switcth between the 2 reference systems. The refrence system you use should concur with the one that you are trying to find. This is found under the Map Datums on the map or from the reference point. That is the trouble most have is not knowing what reference was used. True or Magnetic.Both systems have been used throughout history.

[+Brown Dwarf]

Either will work just fine -- but your compass and your GPS have to be speaking the same language. Use Magnetic North if your compass has NOT been adjusted for local declination; use True North if it has.

 

Other points:

 

Cheap compasses cannot be adjusted.

 

If you cover a wide area, you may find using Magnetic bearings easier than constantly resetting the compass. That's what pilots and sailors often do.

 

Occasionally a cache description will give directions in range/bearing form. Important to know whether the bearing is True or Magnetic, at least in areas where there is a significant difference -- like here in the Pacific North Wet

[+Renegade Knight]

quote:

---

Originally posted by Bushwhacker:

Now what North am I talking about. There are 3 of them.

---

 

There are at least 4 versions of North and I've seen them all used.

 

True North (What we wish a compass would point at so we didn't have to deal with declanation)

Magnetic North (Duh)

Grid North (used by coordinate systems for convenience This doesn't always point north or you would not have a true grid)

Plan North (used by Architects to confuse Civil Engineers)

 

So the answer to the original question is

 

1) North as your GPS tells you since we are all using WGS84 north for geocaching.

2) Use whatever north is most convenient for you when you use your compass to go the last little bit to a cache. Being able to hold a steady bearing is what is imporant here.

3) Use the north the cacher tells you to use when he references north. I've got a cache that says "Use Magnetic North"

4) When in doubt ask.

[+Renegade Knight]

quote:

---

Originally posted by Bushwhacker:

Now what North am I talking about. There are 3 of them.

---

 

There are at least 4 versions of North and I've seen them all used.

 

True North (What we wish a compass would point at so we didn't have to deal with declanation)

Magnetic North (Duh)

Grid North (used by coordinate systems for convenience This doesn't always point north or you would not have a true grid)

Plan North (used by Architects to confuse Civil Engineers)

 

So the answer to the original question is

 

1) North as your GPS tells you since we are all using WGS84 north for geocaching.

2) Use whatever north is most convenient for you when you use your compass to go the last little bit to a cache. Being able to hold a steady bearing is what is imporant here.

3) Use the north the cacher tells you to use when he references north. I've got a cache that says "Use Magnetic North"

4) When in doubt ask.

[+GEO*Trailblazer 1]

When in search, research. I have a bench mark (Tringulation station), whose reference to True North (WGS 84)to another (Triangulation station) was marked at 0 degrees in 1961,it is 1 +- degree now, after the horizontal coordinates were established by classical geodetic methods and adjusted by the National Geodetic Survey in Feb. 2000, The NAVD(National Vertial Datum) 88 height was computed by applying the VERTCON shift value to the NGVD 29 height(displayed under superseded survey control.)The vertical order pertains to the superseded datum. The Laplace correction was computed from DEFLE 99 derived deflections. The Geoid height was determined by GEOID 99.

[+EraSeek]

I much prefer TRUE North, because it is true north. Maps use it with a note on what local declination is so you can adjust your compass bearing to true. Magnetic varies from place to place and even in time. True north never does. That's why they call it true. I like true. It's a good stable thing I can rely on. I can navagate anywhere on earth (in the northern hemisphere) by following the North star which points me to true north. Find out you declination where you are and make the very simple adjustment. Where I am I simply point the needle to 18 degrees east of the N mark, and there I am. The needle point to magnetic north, the N points to true north. My other compass makes it easy by having it perminately offset so my needle now always points to true. (an adjustable declination compass)

 

[+apersson850]

OK, I know I'm biased by my experiences with my Vista, but anyway.

 

For nearly every cache, it doesn't matter which north you use. You can even be an Architect and set your own north, for example in the SW direction, and the GPS will still point its bearing arrow to your destination. If you then are using a unit like the Vista, or any other that has a magnetic compass too, you can keep the unit steady near the cache, and it will still direct you to the cache (assuming sat reception allows it to know where it is, itself), even if the cardinal letters on your navigation screen will seem very unfamiliar.

 

It is only when you

• Interface with any kind of map.
• Use a regular compass together with your GPS.
• Compare directions with somebody elses GPS.
• Follow instructions regarding projections of waypoints, or distances and bearings to walk.

that you need to bother about which north you are thinking about.

 

But if you do care about what the GPS says, use True north. Then you'll not be puzzled about the sun being in the wrong place.

 

Anders

[+apersson850]

OK, I know I'm biased by my experiences with my Vista, but anyway.

 

For nearly every cache, it doesn't matter which north you use. You can even be an Architect and set your own north, for example in the SW direction, and the GPS will still point its bearing arrow to your destination. If you then are using a unit like the Vista, or any other that has a magnetic compass too, you can keep the unit steady near the cache, and it will still direct you to the cache (assuming sat reception allows it to know where it is, itself), even if the cardinal letters on your navigation screen will seem very unfamiliar.

 

It is only when you

• Interface with any kind of map.
• Use a regular compass together with your GPS.
• Compare directions with somebody elses GPS.
• Follow instructions regarding projections of waypoints, or distances and bearings to walk.

that you need to bother about which north you are thinking about.

 

But if you do care about what the GPS says, use True north. Then you'll not be puzzled about the sun being in the wrong place.

 

Anders

[+apersson850]

Trying this out on my Vista, I tested what happened when I set my own north. It turned out that bearings to waypoints are changed accordingly, but not the reported heading.

 

Is this the same for you? No matter what user north setting I try to use, it makes the same result as just setting it to magnetic north, as far as the heading is concerned. Bearings do work correctly.

 

Anders

[dave and jaime]

hey, knight, i am going to up the count to at least 6 different types of north. you didn't mention mills true north and mills magnetic north. if anyone could explain what the hell are the norths are for i would be grateful.

[+apersson850]

Assuming we use degrees, directions are given within the range of 0º to 359º. To know from where to start, i.e. what direction 0º means, we have to define that as north. This is where the alternatives come up.

 

True north: Reference direction is towards the geographical north pole.

 

Magnetic north: Reference is towards the magnetic north pole. In some areas this is about the same, in other areas the difference is large.

 

Grid north: If you have a coordinate system, like UTM or the Swedish grid, the north lines in this grid may not always be aligned with the lines towards the true north. This is because most of these grids are rectangular, but the longitudes curve towards the north pole.

 

User north: If you are unhappy with the other alternatives, just make up your own north. Set it to 90º East, and suddenly east is north, south is east and so on. Could be used if you have a plan over a building site, where you want a logical north to be along a particular wall, for example.

 

The setting of degrees or mils doesn't (actually!) create yet another set of norths...

 

Anders

[+apersson850]

I assumed that User north would allow the User to use whatever north he likes. But it turns out that I was wrong. If you do use User north, you must set it to the correct Magnetic Variation at your location.

 

That's what it's for, and nothing else. If you do enter anything else, you'll get lost. So User north should only be used, if the Magnetic Variation programmed into the device is outdated and incorrect according to some more accurate information source.

 

Sorry for the mistake.

 

Anders

 

[This message was edited by Anders on September 09, 2002 at 08:17 AM.]

[+Criminal]

Cut and pasted from this thread

http://opentopic.Groundspeak.com/0/OpenTopic?a=tpc&s=1750973553&f=3000900883&m=2010917135

 

If anyone is interested in learning how to properly use a compass, check your library or book store for "Wilderness Navigation" by Bob and Mike Burns. It is a very informative book and will explain many of the issues brought up in this thread. It discusses Bruton vs. Silva compasses as well as base plate (Silva style) vs. lensatic (military style). There’s also a small section on GPS. It’s a good read even if there is little immediately relevant to geocaching.

 

If your house catches afire, and there aint no water around,

If your house catches afire, and there aint no water around,

Throw your jelly out the window; let the dog-gone shack burn down.

**Huddie Ledbetter**