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#182109 - 09/13/09 11:34 PM Long/Lat or UTM ??
mtnhiker Offline
Journeyman

Registered: 11/18/05
Posts: 73
Loc: Nevada,USA
Hey folks, I briefly looked for a thread on this but didnt see one.
I was wondering what the general feeling was on using either long/lat or UTM for back country navigation.
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"If it's not with you it cant save you"

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#182111 - 09/13/09 11:55 PM Re: Long/Lat or UTM ?? [Re: mtnhiker]
SARbound Offline
Addict

Registered: 06/08/05
Posts: 503
Loc: Quebec City, Canada
I am in charge of a search and rescue team, and we exclusively use UTM.

Since it's metric, you can estimate distances and stuff by simple arithmetics. 5210780 is 200 meters away from 512980. It's as simple as that.

UTM all the way!
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"The only easy day was yesterday."

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#182112 - 09/13/09 11:58 PM Re: Long/Lat or UTM ?? [Re: mtnhiker]
samhain Offline
Addict

Registered: 11/30/05
Posts: 598
Loc: Baton Rouge, Louisiana
I'm a novice geocacher and I like UTM for the same reason as SARbound.
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samhain autumnwood

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#182114 - 09/13/09 11:59 PM Re: Long/Lat or UTM ?? [Re: mtnhiker]
yelp Offline
Member

Registered: 06/04/08
Posts: 172
Loc: Colorado
Depends on what you want to do with it;'navigation' covers a lot of ground). GPS work? Pencil and paper with a map scale?

I make maps (on a topo base) so when I'm out mapping, ground truthing, whatever, using a scale that's base 10 is much more convenient - especially if it's raining, windy, really buggy, or you're otherwise distracted. I've always used UTMs.

This also holds true for coordinate transforms, like if you're using legacy data that's based off a different datum. Software tends to be more agreeable using UTMs...or at least it's easier for me to see where I screwed up.

I understand that most state agencies (Alaska's one; I don't know about others) use decimal degrees, so if you want to plot a mine shaft or, more importantly, call for an evacuation, having decimal degrees expedites the process. SAR and LEOs please chip in with your experiences! This would be a very good thing to know.

And, as a GIS wizard told me a few years back, UTM stands for "Use This Method."

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(posting this as someone that has unintentionally done a bunch of stupid stuff in the past and will again...)

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#182119 - 09/14/09 12:55 AM Re: Long/Lat or UTM ?? [Re: mtnhiker]
MartinFocazio Offline

Pooh-Bah

Registered: 01/21/03
Posts: 2148
Loc: Bucks County PA
The Search and Rescue folks all seem to like UTM and the pilots prefer Lat/Lon.

I like UTM because its a LOT simpler.

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#182120 - 09/14/09 12:56 AM Re: Long/Lat or UTM ?? [Re: yelp]
MartinFocazio Offline

Pooh-Bah

Registered: 01/21/03
Posts: 2148
Loc: Bucks County PA
Our Medevac folks always asked for decimal lat/long.


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#182126 - 09/14/09 02:15 AM Re: Long/Lat or UTM ?? [Re: MartinFocazio]
scafool Offline
Pooh-Bah

Registered: 12/18/08
Posts: 1534
Loc: Muskoka
One advantage of Lat/Long is that you can get it by sighting on the sun moon or stars as long as you have a watch with you.
If you are good at it you can get your location within about a mile. (1.6 kilometers)with pretty simple tools. Traditional navigators like it more.

That is not accurate enough for fine map work so when you are located on your map and doing survey work you usually use surface measurements. So miles or meters instead of degrees and seconds.
Surveyors like field measurements off grids more than angle measurements from stars.

With the UTM grid system and GPS units available you can locate on a mapped grid to within a few meters easily.
Modern GPS units can locate a surveyor to within 2.5 cm.
As Sarbound points out, with UTM you have an easy distance measurement that you don't really need to think about while with Longitude you have a reading you need to convert to ground measurements.
Universal Transverse Mercator does have a couple of other problems which Yelp's answer points out.
There are many different grids in use and they all vary on where their data points are. The data points (datum) is their model of the shape of the earth. It also involves the grid system they laid over it to measure from.
If you are using the wrong grid system it can throw you off.
The short of this is that you need your maps and GPS unit to be on the same datum. The datum will be noted on your maps.
They also need to be the same for the people you are communicating your locations with.
In North America the standard datum in use is North American Datum 83 which is also used for north America in the World Grid System 84.
However if you have an older map it might be NAD 27. Some USGS maps have grid marks for both. Military grids can be different too.
Usually the difference is only a few hundred meters between NAD 27 and NAD 83.

I think this was a good thread to start.

I use UTM for almost everything. It is easy to measure on a map with a scale card. Most of the time you don't even need the card and just estimating the grid is close enough.


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May set off to explore without any sense of direction or how to return.

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#182134 - 09/14/09 04:37 AM Re: Long/Lat or UTM ?? [Re: scafool]
epirider Offline
Enthusiast

Registered: 12/03/05
Posts: 232
Loc: Wyoming, USA
Myself and Rantor went on a lil adventure today and were using lat/long and we were off by 1/2 mile. We eventually found what we were looking for, but half a mile off??? Next time - UTM!
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is strong enough to take everything you have.
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#182137 - 09/14/09 06:29 AM Re: Long/Lat or UTM ?? [Re: epirider]
Alan_Romania Offline

Addict

Registered: 06/29/05
Posts: 615
Loc: Arizona
Like many have said, UTM is much simpler to use and makes a whole bunch more sense for land navigation.

Also like others have said, pilots like lat/long. On most Garmin handhelds you can set one of the data fields in the trip computer to display Lat/Long even though you may have the GPS set to UTM. This allows me to look up my position in Lat/Long should aviation need it.

It is more complicated if given a Lat/Long coordinate I need to place on my map or in my GPS, but doable (set the GPS to the given coordinate system, enter the coordinates and set back to UTM). However, the biggest issue when two people are using two different coordinate systems is they are often on two separate map datums as well... there is at least one place in AZ where the difference between NAD27 and NAD83 is almost 800m... ask me how I know wink

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"Trust in God --and press-check. You cannot ignore danger and call it faith." -Duke

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#182138 - 09/14/09 06:45 AM Re: Long/Lat or UTM ?? [Re: Alan_Romania]
MostlyHarmless Offline
Old Hand

Registered: 06/03/09
Posts: 982
Loc: Norway
My GPS uses whatever coordinates that are easiest to read on my paper map. In my country, that is UTM, and I think that would be true for the majority of maps in the majority of countries. I consider GPS a very nice addition to paper map and compass, but I take a "I love to use it as long as it works" attitude to the GPS and refuse to consider it my sole or primary means of navigation... Too much that can go wrong.


A nice twist to UTM is the MGRS system:
http://en.wikipedia.org/wiki/Military_grid_reference_system
The essence is that for an accuracy of 100 meters, you only have to deal with 3 decimals in each directions. Ordinary UTM coordinates are 10 decimals. I can remember two numbers of decimals, but not two 10-digit numbers, so it makes life a lot easier. On the maps I use, the kilometer markings are gridded and numbered, so I can read them directly off the page even when the map is folded. My GPS supports MGRS, but not everyone will.


And - switching between the different coordinates systems on your GPS is typically done within seconds, so if one set of coordinate system does not suit you, just switch to another. Make the gadget work for you, not the other way around.

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