Degree Decimal Arrrrgghh

[+Mosaica]

Okay, very basic question here:

 

Take the following set of coordinates:

 

N 43° 29.534 W 072° 26.411

 

The longitude is the first bit: 43° 29.534 and the latitude is the other bit: 072° 26.411

 

Right so far? I can use these numbers in conjunction with my GPSr fine. The part that is confusing me is the last `seconds' part of both lat/long. I'm trying to teach myself about the difference between degrees presented as hrs/mins/secs and degrees presented as a decimal number. The way we use them here at gc.com looks like a hybrid of the two, with the hours & minutes being pretty clear, but the seconds being somehow, er, decimal-y. How can you have more than 60 seconds?

 

I'd like to say that I'm a very precocious 7 year old, but I'm afraid I'm just a dumb 39 year old with large gaps in her education :-) I did search the forum & check the faqs, but no luck so far. Help!

 

Oh, also, do any of you have a super favorite book/manual from which one can learn all about coordinate systems, using maps & compasses, orienteering, etc?

 

Thanks!

 

../Mosaica

[+Stunod]

Geocaching uses the coodinate format of Degrees, Decimal Minutes (DD MM.mmm) not Degrees Minutes Seconds (DD MM SS).

 

In your example, the latitude of N 43° 29.534 is read as "forty three degrees, twenty nine point five three four minutes"

 

If you want to convert it to DD MM SS, just multiply the decimal part by 60: .534 x 60 = 32 seconds, giving you N 43° 29' 32"

Edited May 26, 2004 by Stunod

[+Mosaica]

Oh, right. Thanks! I'd done what you described with another coordinate (44 39.807) and gotten 48.42 seconds and didn't know what to do with the .42. So the above would be read `forty-four degrees, thirty-nine point eight oh seven minutes' and would render as 44° 39' 48" in the hhmmss format, right? Coolio! So, if you're using a hhmmss format to look at some map product, how can you use the extra precision given in that leftover .42? Would it be considered as a, oh, a milisecond or something?

 

../Mosaica

 

P.S. I remember a word from when I was younger --stunod seemed to mean `very drunk' or `very stoned.' The donuts aspect never occured to me. Is there some connection?

[dsandbro]

Complicating the whole DD, DM, DMS thing is people who really should know better (pilots, surveyors, map and compass instructors) use them interchangeably. Written coordinates handed to me include the following examples:

 

40-25-27; 121-55.25

 

39.56.89 x 120.00.36

 

40 25 36 x 121 54.23

 

and my favorite 39 42.5 646125 (mixing a latitude with UTM!)

 

Asking for clarification usually just generates frustration. Ask them which datum they used and you get a deer-in-the-headlights look.

 

I usually ask for their GPS and look it up myself.

[+Stunod]

If the software you are using allows for decimal seconds, enter them. Otherwise round them off.

 

(stunod is Itialian slang for "stupid")

[+Renegade Knight]

If the software you are using allows for decimal seconds, enter them. Otherwise round them off.

 

(stunod is Itialian slang for "stupid")

Exactly. The format doesn't allow for units smaller than a second so you use the decimal seconds if you need to be that accurate.

[Keystone]

This subject is covered very nicely in Markwell's update to the FAQ's. Look for a link to that fine site by going to the Frequently Asked Questions topic that is pinned at the top of this forum. The link is in the very first post, by Jeremy.