6 figure grids

fireman

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Hi guys and girls.
i use a garmin etrex legend just as a back up when in remote areas. can anyone tell me how to convert the location ie sd23456 followed by bearing 23455 into a 6 figure grid ref? i cant understa:nenaund why the garmin only shows 5 numbers insted of 6. i understend all about the different letters in relation to the british o/s grid just not the two groups of five numbers.
any help would be great, or a link
cheers people:nenau
 
Replace the letters with the appropriate OS grid numbers to get a full (12 digit) co-ordinates. It's explained somewhere on the Ordnance Survey website. This explains it fairly well.

HTH

Daniel
 
6 figure map referance

Replace the letters with the appropriate OS grid numbers to get a full (12 digit) co-ordinates. It's explained somewhere on the Ordnance Survey website. This explains it fairly well.

HTH

Daniel

thanks for that daniel, must admit i cant work all this modern gadget stuff.
think i will stick to the good old map and compass.or even better just follow somone else although that is a bit lazy.
 
found the solution

To convert to six figure references simply round the last two digits in each Easting/Northing eg SU 44060 17295 becomes SU 441 173 or SU 44043 17235 becomes SU 440 172
To enter a quoted six figure reference into Memory-Map simply add 00 to each Easting/Northing eg SU 441 173 becomes SU 44100 17300

And its as simple as that. hope it helps anyboby else:JB
 
To explain grid references - needed to navigate the old fashioned map and compass way.

Each pair of letters represents a square 100 km by 100 km so to specify a place to the nearest 100 Km you just need, for example TQ.

Each letter pair is divided into 1 km squares numbered 00 to 99. These are numbered from west to east (called eastings) and south to north (called northings) I teach the easy way to remember which comes first in a definition is E comes before N in the alphabet. Other teach along the corrider and up the stairs - I think my way is easier. These are the grid lines and squares seen on OS maps. To define a location by which 1 km square it is in you need, for example TQ24 78.

This is still a bit vague so we (normally by estimation) divide each 1 km square into squares of 100 metres X 100 metres which means dividing each 1 km square by 10. This means adding a third digit to each pair we used for the 1 km reference. So using TQ 24 78 if we are between 300 and 400 metres to the east of the 24 square we make it 243 (always use the lower number) and if between 600 and 700 metres north of 78 it becomes 786 so the whole position, accurate to 100 metres is TQ243 786.

The above is enough in most cases but there are time more accuracy is needed and each time a digit is added to the original pair we get ten times more accurate. For example instead of saying our position is between 300 and 400 metres east of 24 we actually know it is 370 east and we know it is 620 north of 78 we have an eight figure refence of TQ 2437 7862. This now now accurate to 10 metres. GPS devices normally add one additional digit to get a theoretical accuracy of one metre, therefore TQ24374 78625 would define a position in the TQ square exactly 24 km 374 metres east of the start of the square and 78 km 625 metres north of the start of the square.

Although our GPS may show a ten digit reference we know it is not accurate to one metre so its a bit of a pointless exercise to use that many digits. Ten metre accuracy is possible so using eight digits may be OK then our reference becomes TQ24370 78620 if we use software that requires 10 digits - or just dump the trailing zeros and quote an eight digit reference. Adding two trailing zeros to each pair gets one back to 100 metres accuracy, i.e. TQ24300 78600 or TQ243786.

I did my mountain leader assessment before GPS and was expected to locate a featureless position on a blank hillside to an accuracy of 10 metres. Its possible with a bit of training with a 1:50000 map and a compass but hard to achieve reliably today with gps.

Using the most common OS maps the scale dictates realistic accuaracy. With the popular 1:50000 maps the best we can do without the aid of a magnifying glass and a ruler or Romer scale is 6 digits. With 1:25000 maps eight digits are easier but ten would need very careful measurement and would not normally be needed anyway.

When using OS maps we normally quote six digits without the letters but note the map number as no map covers a big enough area for a reference repeat with different letters.
 
sorted

To explain grid references - needed to navigate the old fashioned map and compass way.

Each pair of letters represents a square 100 km by 100 km so to specify a place to the nearest 100 Km you just need, for example TQ.

Each letter pair is divided into 1 km squares numbered 00 to 99. These are numbered from west to east (called eastings) and south to north (called northings) I teach the easy way to remember which comes first in a definition is E comes before N in the alphabet. Other teach along the corrider and up the stairs - I think my way is easier. These are the grid lines and squares seen on OS maps. To define a location by which 1 km square it is in you need, for example TQ24 78.

This is still a bit vague so we (normally by estimation) divide each 1 km square into squares of 100 metres X 100 metres which means dividing each 1 km square by 10. This means adding a third digit to each pair we used for the 1 km reference. So using TQ 24 78 if we are between 300 and 400 metres to the east of the 24 square we make it 243 (always use the lower number) and if between 600 and 700 metres north of 78 it becomes 786 so the whole position, accurate to 100 metres is TQ243 786.

The above is enough in most cases but there are time more accuracy is needed and each time a digit is added to the original pair we get ten times more accurate. For example instead of saying our position is between 300 and 400 metres east of 24 we actually know it is 370 east and we know it is 620 north of 78 we have an eight figure refence of TQ 2437 7862. This now now accurate to 10 metres. GPS devices normally add one additional digit to get a theoretical accuracy of one metre, therefore TQ24374 78625 would define a position in the TQ square exactly 24 km 374 metres east of the start of the square and 78 km 625 metres north of the start of the square.

Although our GPS may show a ten digit reference we know it is not accurate to one metre so its a bit of a pointless exercise to use that many digits. Ten metre accuracy is possible so using eight digits may be OK then our reference becomes TQ24370 78620 if we use software that requires 10 digits - or just dump the trailing zeros and quote an eight digit reference. Adding two trailing zeros to each pair gets one back to 100 metres accuracy, i.e. TQ24300 78600 or TQ243786.

I did my mountain leader assessment before GPS and was expected to locate a featureless position on a blank hillside to an accuracy of 10 metres. Its possible with a bit of training with a 1:50000 map and a compass but hard to achieve reliably today with gps.

Using the most common OS maps the scale dictates realistic accuaracy. With the popular 1:50000 maps the best we can do without the aid of a magnifying glass and a ruler or Romer scale is 6 digits. With 1:25000 maps eight digits are easier but ten would need very careful measurement and would not normally be needed anyway.

When using OS maps we normally quote six digits without the letters but note the map number as no map covers a big enough area for a reference repeat with different letters.
thanks for that andy, i am quite good with maps but work has asked me to sort a lesson plan out and train half of gmc fire service on the use of gps and maps, got to say it will be a grueller trying to get them to understand it all.
cheers again.
main thing is i know where i am when out on the bike
 
If you need any further advice you could try contacting Ordnance Survey. I used to work for RMC (now cemex) and was responsible for all of the digital mapping data. When we had queries the OS were more than happy to send reps out.
 
I did my mountain leader assessment before GPS and was expected to locate a featureless position on a blank hillside to an accuracy of 10 metres. Its possible with a bit of training with a 1:50000 map and a compass but hard to achieve reliably today with gps.

That's because civvy gps' are only accurate to 33m. Military gps' are slighty more accurate but I can't remember exactly, IIRC it's @15m

Either way, they're only good as long as we keep the yanks sweet. Otherwise they can just shut off the signal.
 
That's because civvy gps' are only accurate to 33m. Military gps' are slighty more accurate but I can't remember exactly, IIRC it's @15m

This info. is somewhat out of date. Garmin spec. states that their GPS units have an AVERAGE accuracy of 15 metres and with WAAS or, in Europe, EGNOS (when it's completely working)an average of 3 metres. Changes to the accuaracy are more a case of atmospheric conditions than anything in the US software. This is why WAAS/EGNOS is used which comprises a number of ground stations to supply corrections. This is accurate enough to be used for blind landing aircraft and although its not commercially used yet the European Space Agency have conducted a number of blind landing tests over recent years.

Some years back the US did degrade the civilian signal and varied the accuracy randomly in order to prevent civvy systems being used against them by unfriendly powers. Then it was useless for any meaningful navigation and I used it to show students how poor it was as they often felt using a gps saved learning how to navigate. The US later changed the software so it could be degraded or turned of in particular parts of the world but was very accurate in others. It was that change that made car mounted satnav systems possible.

Before the change I experimented with using a GPS connected to a computer to show position and it was useless for road navigation as it would often shown an approaching junction which had been passed by as much as 100 metres. Today, although gps cannot be relied on to be within 15 metres I often find the reading is within a few metres of a position I have checked with map and compass and the main reason my map and compass is better in the hills is that there are no batteries to go flat.
 


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