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Degrees, Min & Seconds


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My Magellan GPS 310 is set to LAT LOG, DEG MIN, but it only gives me 2 decimal places, and all geo-cache are to three decimal places. Do I need to upgrade my handset.

 

Or....

 

If I set it to DegMinSec it only counts to 59 on the seconds.

 

I currently have it set to DegMin and this seems to work.

 

Am I needing a better GPS which has three decimal places for the seconds?

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I was reviewing the manual online ... it does appear that you can only go two decimal places. I don't think you need to go the expense of upgrading units right now ... unless you want to. You can always convert to seconds or UTM. I'd probably just do the conversion to seconds. Of course I have a serious gadget problem and this would be the perfect excuse to go buy another ... with more bells and whistles ... GPS!!!!

 

----------------------------------------------------------------

Co-founder of the "NC/VA GEO-HOG ASSOCIATION"

... when you absolutely have to find it first!

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I was curious as to what distance it would amount to by having only the 2 decimal places to work with. With the help of FizzyMagic's new GeoCalc I did a distance calculation based on the following:

 

Presumably the Mag310 rounds off to the closest digit either up or down which means a maximum of .005 minutes difference.

Using N51°31.840, W00°06.400 I added .005 to the latitude and got a difference of 9.272 metres. Adding .005 to the longitude gave 5.783 metres and adding .005 to both is 10.927 metres.

Hopefully I've done it correctly but if so then at almost 11 metres worse case scenario you should be able to find a good number of caches but will make it very difficult on others.

 

Starting off with the 310 will be good practice but just keep an open mind (and eyes) at the cache sites.

 

Cheers, Olar

 

"You are only young once but you can stay immature forever"

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switch to UTM and you will have no problems... you'll be within 3 feet when entering coords of caches you seek

 

as long as it counts down in either metres or feet while in the goto mode, you'll also have no trouble finding...

 

I had a Garmin 12 that DID NOT count down in metres or feet, but in fractions of a km or mile, which made finding a cache more difficult

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I am not sure if I would go to UTM or not. WGS_84 gives ya coordinates sometimes to the second. Witch is to say there are 359 degrees 59 minuets 59 seconds to deal with And just one more second will turn the tables--by one second. (Infendesible) just round things up or down .789= 8 .489=5 .534=5 .298=3 kinda like that GPSers aint that accurate.

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UTM will provide you positions with 1 metre intervals; IT IS THEREFORE more accurate to use UTM than DD:MM.MM

 

Your 310 will do just fine if you use UTM

 

When reporting a new cache though, you will need to convert your UTM into DD:MM.MMM by using an online converter, such as jeeep.com, since pulling it off with only two decimal places from your GPS would be less accurate

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WGS84 is a datum, not a coordinate system.

 

UTM is a coordinate system.

 

WGS84 is the latest and greatest of the datums. This site uses it.

 

My only point is that a Magellan 310, when set to UTM, will do just fine. No need to toss it aside. (The Magellan 310 DOES NOT offer DD:MM.MMM format with THREE decimal places of minutes, it only offers two...)

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Depending on where you are on the globe, that 'third' decimal place equates to as little as 1-2 metres.

 

For example, here are conversions to UTM courtesy of jeeep.com:

 

49:00.000 / -123:00.000 = 500000 / 5427455

49:00.001 / -123:00.000 = 500000 / 5427457

49:00.002 / -123:00.000 = 500000 / 5427459

49:00.003 / -123:00.000 = 500000 / 5427461

49:00.004 / -123:00.000 = 500000 / 5427463

 

and

 

49:00.000 / -123:00.000 = 500000 / 5427455

49:00.000 / -123:00.001 = 499998 / 5427455

49:00.000 / -123:00.000 = 499997 / 5427455

49:00.000 / -123:00.000 = 499996 / 5427455

49:00.000 / -123:00.000 = 499995 / 5427455

 

Similarly, you can see the intervals of the SECOND decimal place, as converted to UTM:

 

49:00.00 / -123:00.00 = 500000 / 5427455

49:00.01 / -123:00.01 = 499987 / 5427474

49:00.02 / -123:00.02 = 499975 / 5427492

49:00.03 / -123:00.03 = 499963 / 5427511

49:00.04 / -123:00.04 = 499951 / 5427529

 

By using the Magellan 310 on the DD:MM.MM setting, like Olar says, you could be out by up to 10 metres.

 

Or, switch it to UTM, and be spot on.

 

One could argue that UTM gives a more precise position than DD:MM.MMM.

 

But 1-2 metres is unlikely to have much impact while geocaching with a consumer grade GPS that has 15 metre accuracy to begin with.

 

If you still wanna sell your 310 and upgrade, I'll buy it for $55 USD.

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quote:
snip

By using the Magellan 310 on the DD:MM.MM setting, like Olar says, you could be out by up to 10 metres.

 

Or, switch it to UTM, and be spot on.

 

One could argue that UTM gives a more precise position than DD:MM.MMM.


Thanks, don't mind if I do argue. icon_wink.gif

Lest we forget, accuracy and precision are related, but not the same. Even though a coordinate may display 1 meter resolution or arc-second to 4 decimal places (DMS.ssss), it does not necessarily follow that you are where it says you are.

UTM showing changes in position in 1 meter intervals would be more precise than DM.mmm, as you state, but not more accurate.

don

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Expanding on Kerry's point if I may to make it clearer, UTM in of itself is not more precise than mm.mmm since mm.mmm is within about 5-6 feet. Although UTM is one meter precise, if you're converting from mm.mmm you're precision is already lost. You would have to start at 4 decimal points to get the precision of the 1 meter UTM.

 

Having said that, with the 310, it would seem if you input the UTM from the geocaching page, you will start with more precision than entering 2 digit minute coordinates.

 

Alan

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quote:
Originally posted by Alan2:

Expanding on Kerry's point if I may to make it clearer, UTM in of itself is not more precise than mm.mmm since mm.mmm is within about 5-6 feet. Although UTM is one meter precise, if you're converting from mm.mmm you're precision is already lost. You would have to start at 4 decimal points to get the precision of the 1 meter UTM.

 

Having said that, with the 310, it would seem if you input the UTM from the geocaching page, you will start with more precision than entering 2 digit minute coordinates.

 

Alan


 

Bingo.

 

My point was that using UTM on the 310 would yield better overall results than using DD:MM.MM

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Maybe UTM might give better results than using DD:MM.mm, maybe not? as perhaps the underlying precision of the coordinates could have some affect. If the underlying position format has some limitations then this would be reflected in any/all convertions and/or transformations

 

Similar with units that can display better precision, even these units will not accept all UTM coordinates precisely as input as through the process of being converted from UTM to lat/Long to cartesian (cartesian being the fundamental GPS position format) then converted back to lat/Long then back to UTM some might notice that what was input is (sometimes) changed by the receiver.

 

With some of these older units (some limited by processor and memory capacity) it's sometimes an unknown if the 2 decimal minute display precision is/was simply a case of that was all that was deemed necessary to output in the days of SA accuracy or limited by hardware in some other way.

 

I don't have access to one but maybe someone with a specific fixed 2 decimal minute format output receiver (like a 310) who has got some spare time then try inputting an incremented (1 metre increments) range of UTM points and note what is echoed back to the display. Just curious.

 

Cheers, Kerry.

 

I never get lost icon_smile.gif everybody keeps telling me where to go icon_wink.gif

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