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Dgm V Os Grid


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Your best bet is to stick with DGM, unless you are capable of doing the relevent conversion on the fly. Most multi or puzzle caches will require you to collect parts of co-ordinates in DGM and having the GPS working in OS grid would be a pain.

 

I don't believe there is any accuracy difference. Happy to be proven incorrect on that one though :-)

 

- Neil.

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We have noticed a significant number of caches where the two co-ordinates given on the details sheet do not tie up. For one cache we visited the WGS84 and OS grid reference were over 100 miles apart. Also, have you noticed that some OS grid refs are missing a number? Dor some caches we've visited the OS grid gave 4 figures for northings and 6 figures for eastings. It turned out that a leading figure was missing from the northings.

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I don't have anything like the experience in the field as some of you guys but since I am stuck at work most of the time I have been fuelling this new obsession by plotting our local caches on MS AutoRoute 2002.

 

I had noticed that a fair number of OS references have a number missing which is impossible to locate without it. In that case I conver the DGM using the Jeeep.com link to a usable format for AutoRoute (Degrees w/Decimal minutes DDM?).

 

However AutoRoute will only accept four decimal places and even when you round up this is less accurate. Yesterday I plotted a new cache with both OS and DDM and the cache could be on either one side of a motorway or the other - D'oh!

 

The Hokesters

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Also, have you noticed that some OS grid refs are missing a number?  Dor some caches we've visited the OS grid gave 4 figures for northings and 6 figures for eastings.  It turned out that a leading figure was missing from the northings.

This is some sort of gc.com bug that has been around for ages. Best not too trust the OS grid ref on the cache pages - use guk.com instead (when it's working!)

 

Lisa

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When I am out caching and using an OS map to find my way around, which is most of the time, I convert my GPS to OS Grid, So I have a quick reference to where I am on the map. When doing a Multi I just convert it back to Datum as it only takes a few seconds to change it.

However when putting co-ords into the GPS I put them in as Datum.

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yo,

thanks everyone for your responses, think i'm getting more of an idea about all this

 

we do lot of walking and use the os map for plotting routes etc.. i brought in the caching aspect to entertain the kids, so i,m plotting routes in os format and attempting to itegrate caches into the walks to stop the kids doing kevin and perry impressions after a few miles!!

 

i'm thinking i'll use the gps in os format so i can relate it to the map, get as close as i can then enter the dgm format and home in from there

 

once again - cheers all your comments are appreciated

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I set the "Show BIG numbers" option of my eTrex Venture's Trip Computer page, and make two of the 4 available fields show position in Degrees and decimal Minutes and UK OS Grid, that way I can compare them at the same time.

 

The OS Grid number is useful for finding your position on the OS maps. Sometimes I believe you will get a discrepancy as mentioned before if your GPSr is using the OS Grid datum instead of the WGS84. Note that the datum used doesn't effect which position format you are looking at. It's all dead confusing to me too.. :lol:

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Sometimes I believe you will get a discrepancy

You'll get a discrepancy all the time - of around 100m!

 

"British Grid" position format is only relevant if you're using "Ord Srvy GB" map datum. Using hddd mm.mmm position format with OSGB datum is useless with the WGS84 references quoted for geocaching. Using British Grid when set for WGS84 datum is equally useless for geocaching.

 

So if you display both British Grid and hdd mm.mmm postion formats simultaneously then one of them is always going to be around 100m out!

 

I don't use an eTrex so apologies if I've misunderstood how you use it or otherwise got hold of the wrong end the stick :lol:

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Also, have you noticed that some OS grid refs are missing a number? Dor some caches we've visited the OS grid gave 4 figures for northings and 6 figures for eastings. It turned out that a leading figure was missing from the northings.

I have come accross this a few times. It's normally zero's missing at the front end of the co ordinates.

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We have noticed a significant number of caches where the two co-ordinates given on the details sheet do not tie up. For one cache we visited the WGS84 and OS grid reference were over 100 miles apart. Also, have you noticed that some OS grid refs are missing a number? Dor some caches we've visited the OS grid gave 4 figures for northings and 6 figures for eastings. It turned out that a leading figure was missing from the northings.

The Geocaching web pages miss out the leading zeroes on the OS grid reference, it is a simple matter to add them to the reference when you enter them into your gps. Remember if only three figures in an easting or northing pad with two zeroes, if four figures add one!

If you search for caches on GeocacheUK, the links to cache pages will have the correct OS grid inserted by Teasels wonderful work.

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"British Grid" position format is only relevant if you're using "Ord Srvy GB" map datum. Using hddd mm.mmm position format with OSGB datum is useless with the WGS84 references quoted for geocaching. Using British Grid when set for WGS84 datum is equally useless for geocaching.

 

So if you display both British Grid and hdd mm.mmm postion formats simultaneously then one of them is always going to be around 100m out!

 

I don't use an eTrex so apologies if I've misunderstood how you use it or otherwise got hold of the wrong end the stick :mad:

I dont know about the Garmin range of gps, but my Magellans can both be set up with a primary and seconary coord system and display both correctly at the same time. However if you wish to enter data in OSGB format you must set your primary datum to OSGB, then if swapping between datums the gps will convert properly for you.

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