Gps Settings Query

[+MMattyK]

Has anyone else noted that if you switch your North reference on your gps that the lat/long readout changes? I only discovered this today.. I went out with two different participants today, I use a Magellan, someone else was using a Meridian, and a third was using an Garmin.

We all had the latest firmware loaded. I was using True North as my north reference, and the others were using Mag North, and our lat/long readouts were not the same. We then all switched to the same North reference, and the readouts all became much closer aligned to each other. I know its probably not much of a difference, but it is a difference.

Should we all be using the same North reference when placing a cache?

What do you think?

[+Birders]

Not sure what you mean by "North reference" as the position of either north or magnetic north is irrelevant to GPS readings.. I don't know about any of the electronic compass gubbins which some GPS' have.. is it to do with that?

 

What you should ensure is that you have WGS84 selected as there may be a slight error if you change to OS Grid.

[+The Bongtwashes]

You should have your GPSr set to :

 

Position Format HDDD MM.MMM

Map datum WSG 84

North Ref MAGNETIC

 

Otherwise where you are won't agree with the published coordinates.

 

Of course, if you're using your GPS for something other than geocaching (yes, I'm told there are other uses!), you should have it set for whichever format, datum and ref. that is most appropriate.

[+Birders]

Presumably all this is for the sake of the electronic compasses?

[+MMattyK]

Thanks for your thoughts 'guys'

 

My reasoning behind using True North, is purely because the magvar differs all over the world, and also changes over time...

The reason I asked was because of the differnces in the lat/long readout on the GPSr when using different North references... and if everyone is useing Mag north as the reference when searching for a cache, I guess that all geocaches should be set to the mag north reference.

Having said that, the differences cant be that great as lots of the older caches were set using wgs84 before egnoss was introduced and operating, and we've all had success to some degree in locating caches.

Just curiousity got the better om me when the differnce was noted.

[+Brenin Tegeingl]

I have my basic Etrex set to magvar so that in a bad lock area I can use a "bearing to" to set the compass that I carry with me. Also I have a cache where you have to go on a bearing for a set distance to get the the cache location, using True North would put you in the wrong location if you use the project a bearing on your GPSr.

 

Dave

[+Learned Gerbil]

I have always used true north as it is native to WGS84 and is consistent with bearings drawn from maps. As the variation from magnetic won't be more than a few degrees in the UK I have always thought it easier to compensate on the few times I need to use a compass to follow a bearing.

All my devices (other than my compass) and software are set to true otherwise how do I know they all assume the same variation?

 

It seems strange to deliberatly set your GPS to be "off" just because a compass is inherently inaccurate. The calculation of the magnetic variation just adds in a fresh and unnecessary variable as far as I can see. Now, if a cache specifies a magnetic bearing, then fine, as long the setter expects people to us compasses and not GPS to find the target, otherwise, what is the point?

 

BTW, this is not a troll, just genuinley confused as to why people add in this unnecessary error.

[+Teasel]

My reasoning behind using True North, is purely because the magvar differs all over the world, and also changes over time...

Magnetic North is useful if you have a compass; Grid North is useful if you have a map.

 

But True North is neither easily measurable, nor does it correspond to the lines drawn on an OS map. So I'm not sure what use you find for it?

 

The position displayed by a GPSr should not depend on which North you choose. If your readings change, it's either coincidence, or you have a defective unit.

[+John Stead]

I did not think there could be any difference in the position shown if the GPSr was changed from Magnetic to True North so ran a short experiment this morning. I took two readings for each of the North settings, averaging each over 300 and repeated this evening. It was clear that the variations over time, i.e. the normal wanderings of the supposed location were greater than any which might have been attributed to the North setting.

But this started me thinking (dangerous ), having read Teasel's remark about True North. I may have missed something but is not Grid North the same as True North if the GPSr is set to WGS84?

[+Brenin Tegeingl]

Here you go John a brief explanation of True, Grid and Magnetic Norths

 

Dave

[SandyGarrity]

Here you go John a brief explanation of True, Grid and Magnetic Norths

 

Dave

 

What Dave said!

 

That really is a good explanation.

[+John Stead]

Thanks Dave - that could not be clearer.