GPS

matt saze Sep 29, 2005 22:41:29

After reading four winds post on the rights of way I checked out his web site. It's an amazing site with some great images.
I was really interested in the gps tips you give and converting the long and lat to OS grid. and vice versa. Is there any way of doing this for british grid?
Also from the MA I tried inputing a waypoint in to my gps from the info on a site, I ended up seriously of course by about 2km when visiting Carn Llechart: http://www.themodernantiquarian.com/site/100. Apart from the fact that gps systems can be inaccurate, are the coordinates displayed in a different way? As when I enter them on to gps there appears to be an extra decimal point or something. Any ideas?
Cheers for your tips. Matt.

Mr Hamhead Sep 29, 2005 23:59:26

Replying to matt saze

Buy a map.

ocifant Sep 30, 2005 07:17:48

Replying to matt saze

Hi Matt, I succumbed to the lure of GPS a while ago. Barely use it these days, but then I don't stray far from the roads...

The easy answer is, if you're in the UK, then enter waypoints in NGR format (available on both TMA and the Portal) and use the OSGB datum. Or get a map :-)

FourWinds Sep 30, 2005 07:22:55

Replying to matt saze

With long/lat there are two way of displaying the value Degrees Minutes & Seconds or Degrees && Minutes with decimal:

<b>Longitude: 3° 53' 9.27" W
Latitude: 51° 44' 23.1" N</b>

<b>Longitude: 3° 53.1545' W
Latitude: 51° 44.385' N</b>

These both represent the same location. When entreing the info you need to either match the format to make it easy by changing the settings on the GPS or convert them to the format that your GPS is set up for.

To convert the second to the first multiply the decimal part by 60 e.g. 0.385 x 60 = 23.1
To go the other way divide the seconds by 60 e.g. 9.27 / 60 = .1545

You are actually best off setting your GPS to use the UK National Grid. Then you can enter the grid refs you find on the web. These are displayed more often than the long/lat reading, although they are becoming more common. Using the National Grid also allows you to get the OS map out and double check that it is at least close!

Take the grid ref for Carn LLechart -> SN698063

To enter this into a GPS you need to convert it into a 10 figure reading SN 69800 06300 . This grid ref should give you an accuracy of 100m, but it is only as accurate as the person that read the map if that's where it came from.

I may enable the code to convert UK grid refs to long lat on megalithomania. It is all there, so it wouldn't take long. As usual the main problem is time!

Grendel Oct 1, 2005 08:57:32

Replying to matt saze

Matt - to answer one of your queries there is a handy grid converter here:

http://www.streetmap.co.uk/gridconvert.html

I have a GPS handset which has helped me find some obscure sites but in a recent British Archaeology there was a website with a free downloadable waymark plotter that was tested to be quite accurate. Useful for making your own plots of circles or working out the relationship between sites in a particular area. I need to make an eBay purchase of the GPS download cable then I'm well away.

Grendel

wolfnighthunter Oct 17, 2005 14:32:29

Replying to matt saze

Just a note,

Spent a couple of days visiting RA around Ilkley, on saturday the fog was very thick, we could only see about 15ft ahead, not ones for giving up, lucky enough i had my trusty gps with me, and even with fog, was able to get all the sites i was looking for. I even managed to get the little Bagder stone to only 4ft out, not too bad in fog..