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Geo location data (1 Viewer)

Farnboro John

Well-known member
Better to ask and be sure. If I understand the system correctly, GPS shouldn't be affected, because it locates you by triangulating your physical position relative to satellites and compares that to a physical terrain database of the globe. Magnetic data isn't involved.

There is an accuracy factor that your navigation system corrects by addressing the most likely result: this does occasionally put you on the wrong street in a cluttered environment with a lot of streets if you haven't got line of sight to more than one satellite (or even one).

Someone will now come along and explain all the ways I am wrong....

John
 

opisska

Jan Ebr
Czech Republic
This really only affects compasses. For centuries, people have known that the compass does not point to the true north, but a bit off, with the angle depending on your position on the planet - potentially huge, if you are very far north/south, but that people only learned laterz when they got there :)

Before the advent of modern technology, there were tables to correct for this effect. Now presumably (I do not have any device with such function personally) you can have a compass, say, in your smartphone and let an app do the correction for you - such app then needs to be updated more frequently as the movement of the magnetic pole speeds up.

I have not yet met a consumer navigation system that actually uses magnetic data for anything, simply because for that purpose, GPS is better. I can imagine people using an app for navigation while walking in nature, where you don't have roads to follow - insuch app you'd have a map and use the compass in the smartphone to tell you where to go. Then this would be affected, but 1. the precision of the bearing gotten this way is probably worse than the error caused by the shift.l an 2. once you start moving, the app will know which way you go from the change of your GPS location and can correct from it.

On the other hand I have no idea how for example ship and aircraft navigation works, I only know that flying has been really conservative in adoption of GPS (because it's not guaranteed to not stop working on a whim of the US Army) so they may be using compasses and have to adjust for this - and I am sure they will because they are really meticulous.
 

Andy Adcock

Well-known member
England
This really only affects compasses. For centuries, people have known that the compass does not point to the true north, but a bit off, with the angle depending on your position on the planet - potentially huge, if you are very far north/south, but that people only learned laterz when they got there :)

Before the advent of modern technology, there were tables to correct for this effect. Now presumably (I do not have any device with such function personally) you can have a compass, say, in your smartphone and let an app do the correction for you - such app then needs to be updated more frequently as the movement of the magnetic pole speeds up.

I have not yet met a consumer navigation system that actually uses magnetic data for anything, simply because for that purpose, GPS is better. I can imagine people using an app for navigation while walking in nature, where you don't have roads to follow - insuch app you'd have a map and use the compass in the smartphone to tell you where to go. Then this would be affected, but 1. the precision of the bearing gotten this way is probably worse than the error caused by the shift.l an 2. once you start moving, the app will know which way you go from the change of your GPS location and can correct from it.

On the other hand I have no idea how for example ship and aircraft navigation works, I only know that flying has been really conservative in adoption of GPS (because it's not guaranteed to not stop working on a whim of the US Army) so they may be using compasses and have to adjust for this - and I am sure they will because they are really meticulous.

So why the need to change some phone navigation systems, they don't work on magnetic North?

I quote from the piece...

'And this rapid movement has required more frequent updates to navigation systems, including those that operate the mapping functions in smartphones'.
 
The British Geological Survey has this article on the use of magnetic and accelerometer sensors in smartphones
A typical smart phone has three magnetic field sensors, fixed perpendicular to each other, which are used to work out the local direction of Magnetic North.

In addition, they have three accelerometers which sense gravity to give tilt information and to help work out which way is down.

What's more interesting is the image at the bottom of this article from the BGS on their WMM showing a Mercator projection of the globe with lines showing the rate of change of movement in the declination of true North.

I just wonder how this affects birds' magnetic sense and migration.
 

DMW

Well-known member
Back in the days when I did a bit of hill walking with map and compass, you had to know what the current map error was. Think it was around 7 degrees, but I believe it has diminished over intervening years as the magnetic pole shifted. At the time, it was "Grid to map, add. Map to grid, get rid."
 
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