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Posted: Wed Dec 23, 2009 12:41 pm Post subject: Using sat nav with road atlas
I'm not a beginner by any means, but I couldn't find a forum which fits this topic.
I would like to be able to use my Tomtom along-side a proper road map. Often, in the middle of a long journey, I think it would be interesting to see exactly where I am on the road map. The TT gives me my location in Lat Long, but there is no easy way to transfer that information to the road map.
I'm currently using a Philip's Big Road Atlas of Britain. The map has numbers 1 to 10 along the bottom and letters up the side, which is no good at all for this, but if you look very closely there are very small numbers as well which I should imagine are to do with Lan and Long, but they bear no relation to what the TT says.
This is an area the map makers should look at, because if your sat nav takes you on a wrong route, along a railway line, up a foot path etc, it is very difficult to put the situation right if you can't find where you are on the map.
Joined: 11/07/2002 14:36:40 Posts: 23848 Location: Hampshire, UK
Posted: Wed Dec 23, 2009 1:26 pm Post subject:
Surely you could just zoom out until you locate a town which would allow you to locate your position on the map?
I really can't see this being something many would need, if anything its an issue for the paper AtoZ publishers who should publish Lat/Lon but I can't see the need.
Anyone who drives along a railway or path will be far too stupid to have had the foresight to have a map handy _________________ Darren Griffin
Joined: Feb 01, 2006 Posts: 2543 Location: Rainham, Kent. England.
Posted: Wed Dec 23, 2009 2:21 pm Post subject:
Quote:
if your sat nav takes you on a wrong route, along a railway line, up a foot path etc, it is very difficult to put the situation right if you can't find where you are on the map.
You could always drive along the line to the next station. _________________ Formerly known as Lost_Property
And NO that's NOT me in the Avatar.
Joined: Jun 04, 2005 Posts: 19991 Location: West and Southwest London
Posted: Thu Dec 24, 2009 6:03 pm Post subject:
Your road atlas is probably using OS grid references which are still widely used on most paper maps.
To convert to Lat/Long, you will need a co-ordinates converter like THIS ONE.
(Might not be much use on the road unless you have internet access somehow, while on the road!)
Also, as a minor point, the OS measurements are based on the OSGB36 reference devised in 1936
Sat Navs base their locations on the WSG84 reference so things will be slightly shifted
Quote:
The longitude and latitude positions on OSGB 36 are the same as for WGS 84 at a point in the Atlantic Ocean well to the west of Great Britain. In Cornwall the WGS 84 longitude lines are about 70 metres east of their OSGB 36 equivalents, this value rising gradually to about 120 m east on the east coast of East Anglia. The WGS 84 latitude lines are about 70 m south of the OSGB 36 lines in South Cornwall, the difference diminishing to zero in the Scottish Borders, and then increasing to about 50 m north on the north coast of Scotland.
The number and letter marking are for Philips own grid for finding towns. The small figures may well be OS reference numbers. Many road maps use the OS grid. I don't know about the Philips one. Will you provide some of the "small numbers" together with a village to which they refer: this would enable a quick check.
There are plenty of downloadable programmes for converting WGS84 to OS grid. One such is from:
http://gps.ordnancesurvey.co.uk/convert.asp
The errors are less than a metre. Twenty years ago there was no error but continental drift has moved Europe from the WGS84 reference in continental america. It is of no significance to us because of the smallness of the error.
A final point on the OSGB36 lats and longs. Although OS maps continue to carry these markings, OS have effectivity abondoned them in favour of a european grid, ETRS89, for surveying purposes. Where I live, near Birmingham, there is a differerence of 97 metres between the them.
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