Magnetic or True

[+brain21]

Hi, I found out that when doing projections, it's good to know if the projection is using true north or magnetic north, or something like that. It makes a big difference. What I'm wondering is if it makes a difference when entering a GPS coordinate and going to that point. Will I end up at different points if I enter the same coordinate in both options (magnetic, true)?

 

Brain21

[+Cardinal Red]

Hi, I found out that when doing projections, it's good to know if the projection is using true north or magnetic north, or something like that. It makes a big difference. What I'm wondering is if it makes a difference when entering a GPS coordinate and going to that point. Will I end up at different points if I enter the same coordinate in both options (magnetic, true)?

 

Brain21

 

When just entering coords and initiating a GO TO, that setting doesn't mean squat. Forget about it.

 

For Projections, or working in conjunction with a map, this needs to be set correctly. This question has been asked a million times already. Soon enough, you will have the opportunity to help someone else clear up the confusion when the question is asked yet again.

[+logger&trail]

Magnetic or true only has a "bearing" (pun intended) when doing projections. As long as you are working in the same map datum a point is a point is a point...

[+ibycus]

To add perhaps a little bit of clarification as to why the above is true, its important to understand the difference between True North and Magnetic North.

A traditional compass will always point to 'magnetic north'. Contrary to what you might thing, this is not the point on the globe at which all lines of longitude meet (i.e. the top of your globe).

Your GPS gives you another option though. Instead of pointing to where the magnetic north pole is, it can point to 'true north' (i.e. the top of the globe).

 

These two locations are different, so the direction to each of them can be completely different (in the extreme case, picture yourself standing on the line connecting true north and magnetic north. The difference between the two would be 180°).

 

When making a projection, you typically tell the person to travel x metres on a bearing of yyy. The bearing is the angular offset between the north reference, and the direction you want them to travel (clockwise from north). Obviously if you're projecting long distances, even a couple of degrees difference can make a big difference in your final location.

 

Another possibility for north reference is 'grid north'. With grid north, you project your coordinates on to some kind of surface and then use the position on that surface relative to a fixed point to map out a grid. Grid north is a reference relative to the alignment of that grid. (Paper maps in Canada are typically 'projected' on to a cylindrical surface, and positions mapped out on there. This is what UTMs are).

 

Dale