Os Grids References In Etrex

[Clarets0]

A friend of mine has bought an eTrex Legend and this is a copy of an email he's just sent to me.

 

"When searching for a place how do you enter the OS coordinates cos there's

only 5 digits after the two letters and then a bng number on line below. OS

coordinates are two letters and SIX digits"

 

Can anyone help me/us out please?

[Alan White]

I agree the presentation is not what it might be, but your friend is under a slight misapprehension.

 

OS grid refs are up to 10 digits long, with 6 and 10 being the most common. Six are used for most things but on a GPS the 100m accuracy of a 6-digit ref would somewhat defeat the purpose of a GPS.

 

So the Legend, like most GPS's I expect, presents all 10 digits. What's unfortunate is that it presents them on two lines like this:

TQ 28557

BNG 79860

 

This is really the grid ref TQ 28557 79860. Or, in 6 digit format, TQ 285 798.

[+littlejim]

OS coordinates are commonly only given with 6 digits which gives you 100 metre resolution. This is adequate for use on an OS map - the 1km squres divide into 10x10 sub-divisions. GPS can do much better than that!

I don't have an eTrex, but it sounds identical to my Geko - the display shows 2 letters (100km square reference) followed by a 5 digit easting. The next line has BNG (ignore) followed by a 5 digit northing. The 5 digits give a resolution of 1 metre.

So, if you have a 6 digit map reference, take the first 3 digits and attach 00 to give the easting (first display line), then the last 3 digits also followed by 00 for the northing on the second display line.

Example: my home easting on the map is 820 - my GPSr shows it as 82078

[Clarets0]

Is there a need to change the datum or do we still use WGS84?

[+Pharisee]

The 'BNG' stands for British National Grid, not Bearing as some people believe.

[Alan White]

Is there a need to change the datum or do we still use WGS84?

You must change the datum, or it will never correspond with the map. The Legend will do it automatically anyway (providing you change the format first, not the other way round).

[Clarets0]

You must change the datum, or it will never correspond with the map. The Legend will do it automatically anyway (providing you change the format first, not the other way round).

Change to which datum? ...and does the yellow eTrex also automatically change datums?

[+Nellies Knackers]

I think it's OSBG36 but someone may correct me.

[Alan White]

Change to which datum? ...and does the yellow eTrex also automatically change datums?

Ord Svry GB.

 

No, the Yellow doesn't change datum when you change the format.

[Clarets0]

Okely Dokely. Got all that.

 

Thanks for the help

[+CuplaKiwis]

Note that you need to change the Position Format to British Grid as well.

[Clarets0]

Note that you need to change the Position Format to British Grid as well.

That was the only bit I knew