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Posted: 5/27/2003 7:45:47 PM EDT
[Last Edit: 5/27/2003 7:46:54 PM EDT by Headless_T_Gunner]
Normally I use UTM coordinates but now I am trying to enter some coordinates using Lat and Lon. The map coordinates give degrees and a decimal point followed by several additional mumbers. For example 95.467832. The coordinate system options in my GPS for Lat/Lon are degrees.min,sec degrees.min/mm degrees.min/mmm which of the above options should I use to enter a coordinate such as the one given in the example? Also what does /mm and /mmm stand for?
Link Posted: 5/29/2003 3:27:14 AM EDT
The way Magellan Displays it, and I think this holds true of Garmin and other brands also: deg.min/mm or /mmm means degrees.minutes.(decimal fraction of a minute in 2 or 3 places) The way to find the minutes from the decimal is pretty straightforward. Just take the integer part (95) and that's the degrees. Take the fractional part (.467832) and multiply by 60. In this case we get 20.06992 arc minutes. That's as far as you need to go for deg.min/mm or /mmm it's just a case of rounding the decimal places to the number of m's. 95deg, 20.07min and 95deg, 20.070min for /mm and /mmm respectively. To get the arc seconds, just do the same to the result of the above. .070 * 60 = 4.1952 Rounding to nearest second is 4 seconds. (some recievers may display fractional seconds, but I haven't found one yet) So in deg.min.sec it would be 95.20.04. Having said all that, I like UTM or MGRS-3 best of all, but for Lat/Lon I use deg.min/mmm because it gives you locations to the thousanth of a degree rather than to a second (1/60 of a degree). I apologize if this isn't completely clear, I haven't written anything in a while and I'm sure it shows. A good question going unanswered while psycho-ex and other crazy threads get all of the posts just seems wrong. Later, Jon
Link Posted: 5/29/2003 3:44:49 AM EDT
95.467832W is a Longitute in decimal degrees. In degrees/min/sec format this would be 95deg [b]28[/b]min 04.1952sec.W (from HP-41C calculator which converts decimal degrees into deg/min/sec) As a surveyor when working w/ Lat/Longs I work w/ as many decimal places as possible. Most use 4 decimal places. I'd used the deg min sec.xxx and enter them as such into the GPS unit as you'll get closer to where ya want to be. Most engineer calculators have a decimal degress to deg/min/sec conversion on them and a cheap one will do this for ya making sure ya get the correct location. [red]JonT - The way to find the minutes from the decimal is pretty straightforward. Just take the integer part (95) and that's the degrees. Take the fractional part (.467832) and multiply by 60. In this case we get 20.06992 arc minutes.[/red] Good explanatiion, wrong result, should be [b]28.06992[/b] Mike
Link Posted: 5/29/2003 4:21:41 AM EDT
Thanks for the correction, I'm using a stack program on my HP48 that switches to the smallest font for anything with a unit attached. That and the darkness of my office and the 8 looks like a zero. Thanks again, Jonathan
Link Posted: 5/29/2003 1:42:40 PM EDT
Thanks for the answers. I was beginning to think that I had finally stumped the board. The UTM system is what I normally use for navigating from topo maps so I have had no practice using lat and lon. Last weekend on an off road event we were given maps with no grid marks or north arrow, just key points marked with lat/lon in the dg.xxxxx format. There were no options in my Magellan nor another persons Garman to read out in this format. So the map was pretty useless since we did not know how to convert to deg/min.sec or deg/min.mm format. Do some GPS units read out in the decimal format? It did not make sense to hand out a map that most people could not use.
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