Occasionally I grab my Garmin hand held GPS unit and head out to the boonies to do some geo-cache hunting. It gives me a good excuse to go tramping around the countryside. This works out pretty well since the geocache website I belong to gives the coordinates of the cache I am hunting for. However sometimes I like to find some other things like old abandoned mines or claim stakes etc. and some of the directions to these places give GPS coordinates. Piece of cake right? Wrong!! The problem is there are different formats for GPS coordinates. Some maps for instance might use decimal degrees like N33.3291 and W111.2277. Try entering these numbers into your GPS unit that uses the decimal minute format. You will notice something fishy right away because you can’t really put the decimal degree numbers into the right places for the decimal minute format. If you just enter all the numbers and not worry about the correct placement you will end up miles away from where you wanted to go.
You need to convert those decimal degree numbers to decimal minute numbers first. Now the same coordinates I personally took from the above actual location look like this--- N33.19.795 by W111.13.922. Yep, that is the same place take or minus a few feet. These coordinates are read like North 33 degrees 19 minutes 795 seconds by West 111 degrees 13 minutes 922 seconds.
So how do you convert decimal degrees to decimal minutes which is what my GPS unit uses? Simply multiply the decimal part of the coordinate by 60 since there are 60 minutes in a degree. So 60 times .3291 = 19.746. So the decimal degree coordinate of N33.3291 is the decimal minute coordinate of N33 19minutes 746 seconds. Which is real close to my actual GPS reading I took out in the field. Close enough for geocaches hunting.
To convert the other way from decimal minutes to decimal degrees simply divide the decimal minutes by 60. I.E. divide 19.746 by 60= .3291. Hot dog, it really works!!! It is the same process for either latitude or longitude. I found the following website that will do the conversion for you and even throw in a map of the area. http://boulter.com/gps/
Now that I have made this all perfectly clear I thought I would throw in some more basic information for those of us who have forgotten everything you ever learned in geography class.
I copied all of this from another website so don’t get disillusioned by my competentness or lack of.
http://www.progeocaching.com/2011/07/gps-and-geocache-co-ordinates/ You might notice I didn’t copy everything because I hate to overwhelm you with information. You are welcome.
“Lines of latitude
We start by cutting the world in half horizontally - this line is called the equator.
Horizontal lines that circle the earth are called lines of latitude.
So if your latitude co-ordinate has an "N" in front of it, then you are north of the equator, and if it has an "S" in front of it you are south of the equator. Going back to the Dead Sea, you can can see that we are located at 31 degrees to the north of the equator. And at the north pole, we would be 90 degrees above the equator.
If, as you move, your latitude numbers increase, in the northern hemisphere you would be heading further north, and in the southern hemisphere you would be heading further south.
Lines of longitude
The line that cuts the world in half vertically through Greenwich in London is called the prime meridian. Vertical lines that circle the earth are called lines of longitude.
Anything west of the prime meridian will have a "W" in the longitude, and anything to the east will have an "E" in the co-ordinate. If, as you move, your longitude numbers are increasing, and you have an "E" in front of your co-ordinate you would be heading further east, and if you have a "W" in the longitude, you would be heading further west.
Alternatively, increasing/decreasing the longitude will move your point due east/west.
Degrees , minutes, seconds
Since the world is circular it can be divided into 360 degrees . However because, as we discussed above, cartographers divided the earth in to north/south, latitudes only go from 0 to 90 degrees in the North or South. Longitudes go from 0 to 180 East or West.
How far is one degree of Latitude?
You'll notice that latitudes are parallel lines wherever you are on earth. It means since the earth is almost a sphere, for geocaching purposes one degree of latitude is the same anywhere on earth .
A minute of latitude is 1/60th of a degree , and one second is 1/60th of a minute.
Geocaching uses Degrees, Minutes and Decimal minutes. You'll sometimes see it referred to as dd mm.mmm, for example in the setup menu of your GPS. Some puzzle caches will use Decimal Degrees to be tricky and these are expressed as dd.mmmm.
So how far is one degree, minute and second?
o 1° of Latitude (1/360th of the Earth's Polar circumference) is 110.5743 km (68.70768 miles)
o 1' (1 minute) of Latitude (1/60th of 1°) is 1.8429 km (1.1451 miles)
o 1" (1 second) of Latitude (1/3600th of 1°) is only 30.7151 m (100.771 feet)
o 0.1" (1/10th second) of Latitude (1/36000th of 1°) is only 3.07151 m (10.0771 feet)
So for co-ordinates in the Degree/Decimal Minute format (dd mm.mmm)...
o If the co-ordinates change by 1 degree you would have moved 110.6 kilometres
o If the co-ordinates change by 1 minute you would have moved 1844 metres
o If the co-ordinates change by 0.1 minutes you would have moved 184 metres
o If the co-ordinates change by .01 minutes you would have moved 18.4 metres
o If the co-ordinates change by .001 minutes you would have moved 1.84 metres.
How far is one degree of Longitude?
Because lines of longitude converge as you get closer to the poles, the distance between longitudes decreases as you move away from the equator and towards the poles. Therefore the distance depends on the latitude at which you are located.
For example at the equator, the distance between degree longitudes (say, between 150 and 151 degrees) is about 111.3 km. However at 35 degrees latitude that distance is only 91.2 km. Of course by the time you reach the pole it's zero.
So you can now calculate distances for decimal minutes in the same way as for latitudes above i. e . At 35 degree latitude 0.1 minutes is 152 metres, 0.01 minutes is 15 metres and 0.001 minutes is 1.5 metres.”
Okay that is probably all you can absorb at one sitting. The quiz will be in 15 minutes. Have fun and don’t get lost.
Here is another website that might be of interest. http://www.brighthub.com/electronics/gps/articles/62785.aspx This is about the same information but presented a bit differently.