CONVERSION OF CO-ORDINATES

[SNAKEBITER]

This mabe a daft question and if it has been covered before then please point me in the direction of the thread, I don't want to waste your time covering the basics (again? ) for the newbies!

 

Give me an OS map and a grid reference and I will get to that point no problems at all. I like to think I am fairly competant with a map and compass, and a GPS. However this is using the british Grid system.

I am having trouble coming to grips with the Longtitude and Latitude references.

 

Example.

 

There is a cache called "Newtimber" 4.5 miles southwest from my home.

Using the british Grid TQ 27048 12449 I can find it no problem on the map.

Using the Co-ordinates N 50deg 53.850 W 000deg 11.684 I can find it (I know that it is 50deg 53.850 North of the Equator and 0deg 11.684 West of the Prime Meridian) on the map.

 

However If I am looking further afield at caches (not yet, I've got to find my feet first!) and all I get given are the Geographic co-ordinates then how am I going to find it?

I can program the co-ordinates into the GPS and use the "goto" feature but I need to be able to find it on a map, or indeed be able to find the relevant map!

 

I am familiar with changing the values in the GPS set-up to use either the British Grid or the co-ordinates so I can follow the GPS but I would like to know what I am doing on paper.

 

It seems I have all the bits of the puzzle but don't know how to fit them all togther! All my map reading "skills" have been completley self taught from books etc so please bear with me.

 

Thanks.

[+MartyBartfast]

Well if you're online you can stick the co-ords straight into Google Maps and it will show you the locale (I don't know if Streetmap/Multimap will take the co-ords too).

 

If you're "in the field" and need to do it, the simplest way I've found is to key the co-ords into the GPSr and then switch it to display British Grid, not forgetting to change the datum to Ord Survey GB (IIRC), then show the waypoint and it will be in the OS grid format.

[+lordelph]

Doing the sums on paper is not for the faint hearted, involving something called a Helmert Transformation, and, for all I know, the sacrifice of a goat. (A quick google found this description)

 

For all your coordinate conversion needs, I recommend Barry Hunters www.nearby.org.uk site. Pretty sure no goats are harmed that way.

Edited November 25, 2006 by lordelph

[SNAKEBITER]

Thanks!

 

I love the new technology but being bit of a luddite I feel there is no substitute for a sound knowledge of land navigation with the basic equipment. I was surprised to read in some of the other threads that some people carry laptops around to download information as they go I couldn't hack that!

Minimalist, thats my approach to most things.

[+douglasf]

When I first started caching I used OS Grid in the GPS for the same reason. However I kept finding myself 100m of so adrift - it turns out there is some issue with a direct conversion from OS to L/L. I later learnt that there is a reference issue between the two formats (see here). It's not a major issue until you get to a multi-cache. Also note the 1:25K (orange) maps do have long/lat printed down the extreme sides.

 

Thinking again it's not unusual to find myself 100m adrift of the right place nowadays but thats just me having finger trouble with my GPSr I think

[Deceangi]

On every cache page is the OS grid reference. For Traditional caches this is the posted coordinates. The final container for a multi, generally will be within a couple of miles of that [occasionally it can be further away, but the cache page will usually hint or inform you of that] . Puzzle caches are within 3 miles of the posted coordinates, with rare cases over that distance [where the placer has presented a good case to the reviewer to allow it].

 

Also if you enter your home coordinates into your profile [which does not have to be your home, but a nearby location such as a road junction, park or shopping centre] you will get a distance and direction to the posted coordinates from your home location. Your home coordinates can not be seen by anyone else, and is a requirement if you place a cache, as the reviewer will see a distance from your home coordinates to the cache placement. Which is used in the review process, to assess for vacation caches or those over a reasonable distance and so requiring a maintenance plan.

 

Welcome to the insanity consensus is that once you've found 10, your hooked for life

[+Pieman]

A good utility for converting Lat/Long to various formats is Waypoint Workbench.

 

If you want to map Lat/Long coordinates you can do this at Streetmap where there is an option to put in coordinates. Remember to convert to degrees:minutes:seconds. Thus, N53 22.500 becomes 53:22:30 ie you multiply 0.500 by 60 to get the seconds. Also remember that West coordinates are negative in their system.

Edited November 25, 2006 by Pieman

[+kewfriend]

EASY METHOD

If you have MS Autoroute, then the 'find' can be entered either in decimal or in British Grid. eg. N51 33.456 would be entered as 51.557 - note Westings are minus numbers. The neat bit is that you now click the OS Tab in the find and the UK OS Grid ref is displayed. Annoyingly the full same trick doesnt work in reverse. Enter the location on the OS tab on the find, and confirm so that you end up up seeing the pushpin on the map itself. Then you can use the 'locator' tool passing it over the found location on the map and it displays the Northing and Westing.

 

Otherwise you the freebie QUEST Grid InQuest - which is a bit tedious but very accurate.

Edited November 26, 2006 by kewfriend

[barryhunter]

For all your coordinate conversion needs, I recommend Barry Hunters www.nearby.org.uk site. Pretty sure no goats are harmed that way.

 

... I can categorically deny any Goat Sacrifices in the making or running of the site

 

As mentioned unless you have a ipaq/palm or other pocket computer the by far the simplest method is to use the GPS to do the maths for you. I did once see a rough and ready paper version (about 5-6 minutes per conversion however!), but was only accurate to about halve a kilometer.

 

Also while many OS paper maps do have a Lat/Long graduale in the margin, this is on the OSGB datum, so if using it transferring between Map <-> GPS you will need to set the GPS appropraitely, but as the 'standard' datum is WGS84 (as used in Geocaching) its simpler not to bother and get the two Lat/Long datums mixed up easily 200m errors can result.

 

Aside from Multis and Puzzels etc that often quote Lat/Long figures, you can just have the GPS in Lat/Long WGS84 mode when transferring the Waypoints before setting out, and then leave the machine in OSGB Grid Refs, while in the field. (for referring to the map) [the same in reverse can be used in setting, but extra care needs to be observed that you get the datum settings correct]

[SNAKEBITER]

Thanks for all this help!

I had my first find today using O/SGrid reference today which I am well chuffed with!

There is too much information to digest here in one go so I'll have a look at work tomorrow. It doesn't help that I've a little drinkies to help celebrate my first find

 

Thanks again for the help.