UTM, Latitude Longditude....

stevebuk · Occasional Visitor Joined: Jun 16, 2004 Posts: 22

Hi all,

Sorry for what is probably a very, very basic question... On my GPS I see reading such as N50 54.7005 W1 20.9209 for example. Is this UTM? Do all GPS programs record like this. Just I want to get some paper OS maps and start to learn how to use this thing and having read some posts I see talk of both UTM and latitude / longditude and wanted to know what it is my GPS shows and if I buy some maps will they show places using the same format?

Sorry if this is very basic.

Thanks
Steve

Hunnymonster · Posted: Sat Jun 19, 2004 9:32 pm Post subject:

Most GPS receivers default to WGS84... what you're seeing there is 50°54.7005'N 1°20.9209'W (50°54'42"N 1°20'55"W in sexagesimal)...

In the UK OS Landranger maps have Latitude & Longitude marked on them at 5' intervals - but because the grid datum and projection used for the maps isn't WGS84 it's skewed slightly diagonally.

It is possible to convert a Lat/Long into an OSGB grid reference (or indeed a UTM reference) but unless you can get your device to output in the mode you want, you'll probably need a calculator tool to do the conversion for you.

stevebuk · Occasional Visitor Joined: Jun 16, 2004 Posts: 22

Hi there,

Thanks for the quick reply. So WGS84 is a "sort" of lattitude longditude? But it is different slightly to the OS maps? Do you know a web page that can convert? If a friend was to email me some waypoints, how do i know what they are in?

Kind regards,
Steve

Hunnymonster · Posted: Sat Jun 19, 2004 10:08 pm Post subject:

http://jeeep.com/details/coord/ is one for WGS84/NAD27 to UTM

http://www.tandt.be/wis/ is those and lots more (but not OSGB)

http://www.gps.gov.uk/additionalInfo/gpsSpreadsheet.asp should have enough to get on with the OSGB/WGS84 translation.....

There are also many (some highly technical and/or theoretical) references out there if you're interested - but it all boils down to the fact that the earth isn't a perfect geometrical figure, so some representation of it has to be made for whatever purpose you want your mapping for.... and any 2 dimensional representation (like an OS map) is going to have inaccuracy in dimensions inherent because of the 'loss' of the curvature of the earth in translating to a flat paper map - thankfully over the coverage of a landranger sheet those distortions are small!

oddsock · Posted: Sat Jun 19, 2004 10:10 pm Post subject:

Hi, I don't know if this is what you require .Registration is needed to access the data!! http://www.gps.gov.uk/

dave

stevebuk · Occasional Visitor Joined: Jun 16, 2004 Posts: 22

Many thanks for all the replies.

Very helpful.
Steve

Privateer · Posted: Sat Jun 19, 2004 11:06 pm Post subject:

Hi Steve,

If you want to use your GPS unit with Ordnance Survey (OS) maps then you may need to set the GPS to the following:

Position Grid: British Grid
Map Datum: ORD SRVY GB (OSGB36 is the same)

If you need a quick refresh on reading OS maps and using the National Grid, then Ordnance Survey do a very good interactive guide, which can be seen here.

Once you’ve done the above you will find that you be able to locate your physical position with your GPS unit and thus accurately determine your position on the OS map. Thumbs Up

The above can be done with most paper maps of any part of the world, as long as the map states which Map Datum to use and also the Position Grid.

If you look at the menu of your GPS you will see loads of different Map Datums, one that is often used for maps is the Datum WGS84. You will also see different Position Grids on your GPS to choose from the main one is Longitude & Latitude, you will also see UTM (Universal Transverse Mercator). Smile

Regards,
_________________
Robert.
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stevebuk · Occasional Visitor Joined: Jun 16, 2004 Posts: 22

Thanks,

Just what I wanted :D

Steve

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