GPS North Reference

Richard Phillips

Hello all,

What do you all tend to use as your North reference with your GPS; True,
Grid or Magnetic?

My GPS defaults to True. I suppose I normally orientate my map to make the
grid lines point to True (taking magnetic variation into account) (I don't
tend to take the Grid/True variation into account), so it makes sense that
my GPS should use True also?

Any thoughts?

Regards,
Richard.

Paul Saunders

Richard Phillips wrote:

> What do you all tend to use as your North reference with your GPS;
> True, Grid or Magnetic?

Magnetic. It's rare that I use a compass these days, but if I do, I use it
in conjuntion with my GPS, therefore it's handy to set it to magnetic so
that you don't have to convert between the two.

If you think about it, it doesn't really matter what GPS north is set to. If
you've entered waypoints you simply follow the arrow to get there, the
bearing number is irrelevant, unless you want to correlate it to something
else, like a compass.

If you want to correlate it to the map, then set it to grid north, but why
would you need to do that? Just enter the grid ref of where you want to go
and follow the arrow.

Setting it to true is pointless IMO, since neither the map or your compass
will correspond to that.

> My GPS defaults to True. I suppose I normally orientate my map to
> make the grid lines point to True (taking magnetic variation into
> account) (I don't tend to take the Grid/True variation into account),

But the grid lines don't point to true north, so you should take the
grid/true variation into account, if you want to be really accurate, but
that's just making more work for yourself.

> so it makes sense that my GPS should use True also?

I can't think of a good reason to use true, unless you're trying to reach
the north pole.

But what has orienting your map got to do with anything? You're not trying
to use your GPS like a compass, are you? If so, you may as well use a real
compass. If you're using a GPS, just enter a grid ref and follow the arrow.
Then it doesn't matter what bearing the GPS reports.

The only time I use a compass with my GPS is if I'm moving too slowly for
the GPS direction arrow to point in the right direction (very steep or rough
ground). In such a case, the GPS still knows where I am and where I'm going
to (the waypoint I'm heading toward) and thus reports the bearing to the
target, even if the arrow doesn't point the right way. So I can simply read
the bearing and use the compass to follow it, which is why I set it to
magnetic.

Paul
--
http://www.wilderness-wales.co.uk/
http://www.wilderness-wales.co.uk/weblog/
http://www.wilderness-wales.co.uk/w...y/comet-holmes/

Dominic Sexton

In article <5pWdna4B1Yfaa87anZ2dnUVZ8rednZ2d@pipex.net>, Paul Saunders
<pvs1@wildwales.fsnet.co.uk> writes
>Richard Phillips wrote:
>
>> My GPS defaults to True. I suppose I normally orientate my map to
>> make the grid lines point to True (taking magnetic variation into
>> account) (I don't tend to take the Grid/True variation into account),
>
>But the grid lines don't point to true north, so you should take the
>grid/true variation into account, if you want to be really accurate, but
>that's just making more work for yourself.

The mag var given on OS maps is between grid and mag north. Newer maps
may also give a value for the difference between true and grid. So it
depends where Richard is getting the mag var from but if it is from the
OS map he's not doing quite what he thinks. There is generally no need
to worry about true when using an OS map with a compass or GPS.

The further one is away from the central meridian (2 degrees west which
very close to the western edge of the Peak District) the greater the
difference between grid and true.

To answer Richard's question I would use mag if I were using the GPS
with a compass and grid if just with the OS map. I would only use true
if I was using it with a map with true north lines on it.

--

Dominic Sexton

Paul Saunders

Dominic Sexton wrote:

> The further one is away from the central meridian (2 degrees west
> which very close to the western edge of the Peak District) the
> greater the difference between grid and true.

Indeed, checking my Swansea map it seems the grid/true difference is 1.5
degrees E and the current mag/grid difference is 2.5 degrees W, making a 4
degree difference from mag to true.

Paul
--
http://www.wilderness-wales.co.uk/
http://www.wilderness-wales.co.uk/weblog/
http://www.wilderness-wales.co.uk/w...y/comet-holmes/