Which is better to use....Magnetic North or True North

[+Raven02]

Or does it matter?

 

Thanks

[+Renegade Knight]

Doesn't matter.

 

The GPS pointer points at the cache. It may matter if you project a waypoint. I've tried to do that once in 1000 caches and it wasn't for a cache.

[+Kewaneh & Shark]

True or magnetic would not matter if you are simply going to a particular waypoint, such as a cache. It would make a difference if you are planning on using your GPSr as a compass. The difference between true & magnetic north - called Magnetic Deviation - in your area could be substantial. The result of following an incorrect compass bearing could be equally as substantial. If you are planning on using your GPSr to follow some sort of compass bearing, it would be important to know how the bearing was derived (from magnetic or true north) and set your GPSr accordingly.

 

Magnetic Deviation does vary depending on what part of the globe you are on. The deviation also changes over long periods of time. A map of the Geomagnetic Reference Field of North America can be seen HERE. Additional info about the Earth's magnetic field can be found on the USGS National Geomagnetism Program website.

 

- Kewaneh

[+BlueDeuce]

For the basic park or city caches I'm more concerned about North when I'm using a roadmap than when I'm walking down a gravel trail, so true North more often than not.

[+bigeddy]

Or does it matter?

All directions are relative so the answer depends on your purpose. There is no such thing as "true" north. What we call True North, Geographic North or Map North is just a standard way of making maps. Magnetic North refers to a moving dipole in the earth. And then there is Astronomical North which relates to the moving axis of rotation of the earth.

 

Because I used a compass long before the GPS, I find Magnetic North easier to use in the field. When I had paper topo maps, I would draw the magnetic lines on them. Orienteering maps already point to Magnetic North so that you do not have to fuss with declination.

 

Note, though, that the earth's poles move over time and so does the declination at a given location. Many topo maps date to the 60's when the declination where I live was nearly 4 degrees greater than at present (20 versus 16). Big difference for precise navigation!

 

I have done many offset caches and multi-caches with projected coordinates using both True and Magnetic. They are great fun and more interesting to me than puzzle caches that have nothing to do with navigation. For caches either True or Magnetic are fine but the cache description should say clearly which is used.

[+D0T-C0M]

sorry for getting a little off track, but while reading through this thread a question popped up. I was wondering when the meteologists give the weather and give wind direction I'm I correct in assuming they are using magnetic north as a reference?

[+budd-rdc]

sorry for getting a little off track, but while reading through this thread a question popped up. I was wondering when the meteologists give the weather and give wind direction I'm I correct in assuming they are using magnetic north as a reference?

 

That's a good question. Looking at the weather maps they use, though, they often show the lat/lon grids, which are True North based. It would be interesting to see what the answer is.

 

As for the OP, it doesn't matter which one you use, but personally, I prefer True North since it's convenient when I'm using maps, or trying to guess a direction based on street grids.

[+gpsjeep]

If your searching for a cache and the cache owner had his gps set to true north when placing the cache and you are trying to find it with your gps set to magnetic north you can be off enough to where you won't find the cache.

I went looking for a cache of mine to do some maintenance and I couldn't figure out why I couldn't find it. Some how I had changed my gps from magnetic to true. After I fixed the problem and changed it back to magnetic, I found I was about 80 feet off. So it can matter.

I would fare to say that I think most caches are hidden using magnetic north.

You say tomato I say tomaaato.

 

-Jeff

[Grasscatcher]

Surely you jest.....!

 

Coordinates of a specific location are not influenced by whether you have your GPSr set on Magnetic or True.....

 

Maybe you had tomaatoes in your ears and couldn't hear what your GPSr was telling you.....

[+EScout]

Surely you jest.....!

 

Coordinates of a specific location are not influenced by whether you have your GPSr set on Magnetic or True.....

 

Maybe you had tomaatoes in your ears and couldn't hear what your GPSr was telling you.....

Three of the caches I have placed are very much influenced by setting your GPSr to Magnetic or True. I specify True for these and if you use Magnetic, you will not find them.....they are navigational multi-caches.

[+EraSeek]

sorry for getting a little off track, but while reading through this thread a question popped up. I was wondering when the meteologists give the weather and give wind direction I'm I correct in assuming they are using magnetic north as a reference?

 

Great question! But True would have been my guess and this link seems to show true is used: http://www.ndbc.noaa.gov/station_page.php?station=51002 note that the active wind direction is given in compass bearing (E) but it is specified as ( 90 degrees True).

[Alphawolf]

Or does it matter?

 

Thanks

 

This simple:

If you are using your GPS with a compass...Use mag. north

If you are using it with a map...Use true north

If you are using it by itself...It doesn't matter one bit

[John E Cache]

True or magnetic would not matter if you are simply going to a particular waypoint, such as a cache. It would make a difference if you are planning on using your GPSr as a compass. The difference between true & magnetic north - called Magnetic Deviation - in your area could be substantial. The result of following an incorrect compass bearing could be equally as substantial. If you are planning on using your GPSr to follow some sort of compass bearing, it would be important to know how the bearing was derived (from magnetic or true north) and set your GPSr accordingly.

 

Magnetic Deviation does vary depending on what part of the globe you are on. The deviation also changes over long periods of time. A map of the Geomagnetic Reference Field of North America can be seen HERE. Additional info about the Earth's magnetic field can be found on the USGS National Geomagnetism Program website.

 

- Kewaneh

Up here we call it declination not deviation. This year our declination is 17.0 degrees east in Portland. I had a really hard time figuring out which way to point my HDTV antenna given a bearing from a web site. I finally put the tower waypoints in EastGPS to figure it out with a compass. Recently I turned on the compass on my 60csx in my living room with a tower waypoint and I got my best HDTV signal ever by pointing the antenna the direction of the compass arrow. Edited October 31, 2006 by John E Cache

[+gpsjeep]

Surely you jest.....!

 

Coordinates of a specific location are not influenced by whether you have your GPSr set on Magnetic or True.....

 

Maybe you had tomaatoes in your ears and couldn't hear what your GPSr was telling you.....

 

You are funny. I haven't had tomatos in my ears since our last 4th of July picnic.

 

True north and magnetic north are two different locations on the earth. Close, but not the same location.

True north is a constant and refers to the geographic North Pole. Magnetic north tends to shift and refers to the pole of the Earth's magnetic field.

Therefore, if you set a waypoint according to magnetic north and a waypoint according to true north the exact location will not be quite the same.

 

-Jeff

[VoltageHz]

So what is it? Will it effect a waypoint or not?

 

I've always read that it won't, but now people are saying that it will.

 

We need conclusive evidence!!

[+YuccaPatrol]

sorry for getting a little off track, but while reading through this thread a question popped up. I was wondering when the meteologists give the weather and give wind direction I'm I correct in assuming they are using magnetic north as a reference?

 

I think that "North" just means "the top of the map" to meteorologists. The generally subtle differences between true and magnetic north just don't come into play when you are making forecasts based on estimations and approximations with very little accuracy when compared to GPS-type accuracy.

 

The compass 360 degrees, but I have never ever seen wind direction described using anything more than the 16 basic directions (N,S,E,W, NW, SW, SE, NE, NNW, NNE, etc).

Edited October 31, 2006 by YuccaPatrol

[Grasscatcher]

Ah Ha! See, now the rest of the story comes out!

 

Yes, Navigationally speaking, magnetic vs true makes a difference., but the "end" coordinates of a specific point will not be affected.

 

However, on navigation caches, the original placer definitely should specify whether the directions are in Mag or True, not just make the cacher guess.

 

If the instructions are done correctly, the final location will have the same coordinates either way, but the path (bearing) you took to get there will be different. (Compass Angle of the path from A to B to C)

[+BadAndy]

Surely you jest.....!

 

Coordinates of a specific location are not influenced by whether you have your GPSr set on Magnetic or True.....

 

Maybe you had tomaatoes in your ears and couldn't hear what your GPSr was telling you.....

 

You are funny. I haven't had tomatos in my ears since our last 4th of July picnic.

 

True north and magnetic north are two different locations on the earth. Close, but not the same location.

True north is a constant and refers to the geographic North Pole. Magnetic north tends to shift and refers to the pole of the Earth's magnetic field.

Therefore, if you set a waypoint according to magnetic north and a waypoint according to true north the exact location will not be quite the same.

 

-Jeff

 

The location has nothing to do with a compass or map bearing, true N or mag N. It's a fixed spot on the earth using a grid. Navigating to that point is different. If you're using a compass or a map, you better get your Norths correct or you may miss it. If you're using a gps or a bloodhound.... it doesn't matter.

 

Projected waypoints are another story entirely as you need to know what reference the waypoint marker used and either match his reference or do the math.

[+Renegade Knight]

Surely you jest.....!

 

Coordinates of a specific location are not influenced by whether you have your GPSr set on Magnetic or True.....

 

Maybe you had tomaatoes in your ears and couldn't hear what your GPSr was telling you.....

Three of the caches I have placed are very much influenced by setting your GPSr to Magnetic or True. I specify True for these and if you use Magnetic, you will not find them.....they are navigational multi-caches.

True or Magnetic matters for a following a bearing. However then it's up to the cache owner to tell us which to use. Which you have done.

[+Renegade Knight]

So what is it? Will it effect a waypoint or not?

 

No it won't. Your waypoint is defined by WGS 84. That system already has north built into it. Plus it's a point on the ground and not a direction. As long as I used WGS 84 when I set the cache, and you use WGS 84 when you seek the cahe you will get to the same point. The only variable is the accuracy of the GPS units we both use.

 

If I have to go a point and then follow a bearing to another point (where the 2nd stage of a multi cache is located) then I need to know what that the bearing is based on so I know I'm heading the right direction. In other words, just like in caching where everyone uses WGS 84 (which defines the coordinate system used) we have to define the bearing system used.

 

http://academic.brooklyn.cuny.edu/geology/...inksa/comp.html

This link shows one way to do bearing descriptions.

In this system North is NORMALLY Grid North which is close to true North but not quite the same. Still it's specified in the basis of bearing.

 

You can also use Azimuth.

http://en.wikipedia.org/wiki/Azimuth

If you do, then it's critical to specify True North, or Magnetic North as the North you are basing your bearing on.

 

Just to confuse people you can also make your own basis of bearing between two land marks and call it anything you want. The math will work...if you undertand what a basis of bearing is and that it doesn't have to have anything at all to do with true and magnetic north as long as it's defined so people can figure it out.

[+JSWilson64]

...The GPS pointer points at the cache. ...

 

Mine always points where the cache is supposed to be. Then my kid points to the cache, somewhere I'm not looking.

Edited October 31, 2006 by JSWilson64

[GreatCanadian]

Magnetic North or True North WILL NOT AFFECT THE COORDINATES OF A WAYPOINT!! Your map datum will, but let's assume that for now we're dealing with the same map datum. Take this example. Let's assume you and your buddy are both using a gps (1 each). You have marked the coordinates for a geocache, rock, pole, whatever. The next day, you and your buddy set a go-to to return to that spot. Your gps is set to true north, and your buddies is set to magnetic. Your gps will tell you a particular bearing to get to that waypoint. Your buddy's gps will tell him a bearing that differs from yours. If you were in my area, his gps would indicate a bearing that is 21 degrees higher than yours, as magnetic declination in my area right now is 21 degrees west of true north. BUT BOTH GPS'S WILL TAKE YOU TO THE SAME SPOT (all other things being equal). True or magnetic does not affect the waypoint, it just shows a different bearing to get there. Also, if you and your buddy had the North reference set differently when marking the waypoint, it still wouldn't make a difference.

 

On a gps with the north reference set to magnetic, if you travel at zero degrees (or 360 degrees) you would be travelling towards magnetic north, which is 21 degrees WEST of true north (in my area). To travel toward true north with this gps you must add 21 degrees to the bearing, and travel at 21 degrees. On a gps with north reference set to true, you must travel at zero degrees (or 360 degrees) to travel toward true north. Therefore, even though both gps's are travelling at different bearings, they are both travelling in the same direction, and approaching the same point.

 

As for using a regular magnetic compass, I always used true north even before the gps became popular. You can buy magnetic compasses that can adjust for magnetic declination. Using a compass in this manner makes it much easier to take bearings from a map - like a topographic map, on which the sides of the map are oriented to true north. The gridlines are neither true north nor magnetic - although they do coincide at times. And magnetic north, although indicated in the map legend is not that useful for 2 reasons. The lines are not drawn on a topographic map (you can draw them, but why would you when you already have true north reference from the map borders), and magnetic declination changes, meaning that on maps that are more than a few years old, the indicated magnetic declination is not accurate.

Edited October 31, 2006 by GreatCanadian

[+Alan2]

The lines are not drawn on a topographic map (you can draw them, but why would you when you already have true north reference from the map borders),

You would draw the 1000 meter grid lines on a quad map so you can find a particular coordinate location uising the UTM coordinate system. Many of these maps now come with these lines drawn in. If not, you can draw them yourself connecting the tick marks at the map borders.

Edited November 1, 2006 by Alan2

[+EraSeek]

True or magnetic would not matter if you are simply going to a particular waypoint, such as a cache. It would make a difference if you are planning on using your GPSr as a compass. The difference between true & magnetic north - called Magnetic Deviation - in your area could be substantial. The result of following an incorrect compass bearing could be equally as substantial. If you are planning on using your GPSr to follow some sort of compass bearing, it would be important to know how the bearing was derived (from magnetic or true north) and set your GPSr accordingly.

 

Magnetic Deviation does vary depending on what part of the globe you are on. The deviation also changes over long periods of time. A map of the Geomagnetic Reference Field of North America can be seen HERE. Additional info about the Earth's magnetic field can be found on the USGS National Geomagnetism Program website.

 

- Kewaneh

Up here we call it declination not deviation. This year our declination is 17.0 degrees east in Portland. I had a really hard time figuring out which way to point my HDTV antenna given a bearing from a web site. I finally put the tower waypoints in EastGPS to figure it out with a compass. Recently I turned on the compass on my 60csx in my living room with a tower waypoint and I got my best HDTV signal ever by pointing the antenna the direction of the compass arrow.

 

Deviation

The error in reading a bearing from the compass caused by the magnetic influence of some nearby object, such as a metal post or a car parked beside you. In the case of boats it may even be due to the materials from which the boat is constructed. Electric currents close to the compass will affect its behaviour. To avoid this type of error the compass should be kept away from all such influences. Most boats have some measure of deviation which should be minimised by careful mounting of the compass. Deviation changes each time the boat alters course. There are people skilled in compass adjustment who can issue a card for a particular compass with deviations listed for changes in direction.

 

Declination (also known as variation)

The error caused by the earth's magnetic field. For a magnetic compass, the needle will point towards magnetic north rather than true north. Depending on where you are on the earth's surface this difference may be as much as 30°. Variation (declination) may be to east or west of true north, again depending on where you are on the earth's surface. In Queensland variation (declination) is about 11° easterly. Variation (declination) also changes as time progresses (as the magnetic north pole changes position). This information is always shown on maps and charts (usually in the compass rose) with a base year and a statement to say 'increasing...... each year'.

[GreatCanadian]

The lines are not drawn on a topographic map (you can draw them, but why would you when you already have true north reference from the map borders),

You would draw the 1000 meter grid lines on a quad map so you can find a particular coordinate location uising the UTM coordinate system. Many of these maps now come with these lines drawn in. If not, you can draw them yourself connecting the tick marks at the map borders.

 

Yes sir, the 1000 metre grid lines are already drawn on our topographic maps here in Canada, and correspond to grid north. If you read the post just a little more losely you would see that I was referring to the lines that would parallell magnetic north. The UTM reference is calculated from the gridlines representing grid north, not magnetic north. Again, grid north and true north remain constant, magnetic north changes.