Geography Reference
In-Depth Information
These are the GPS' current location expressed as degrees and minutes. Deciphering them
is not hard once you get used to it, but it can be a little strange at first.
The format of the string is
DDMM.mmmm
for the latitude (vertical) direction and
DDDMM.mmmm
for the longitude (horizontal) direction.
Starting with the north (latitude) measurement in the string, the first two digits are the
number of degrees, and the remaining numbers are the minutes. The numbers after the
decimal point are fractions of a minute. This gives us:
53 degrees, 21.5802 minutes north
For the longitude measurement, the first
three
digits are the number of degrees, and the
remaining digits are the minutes. All the numbers after the decimal are fractions of a minute.
This gives us:
6 Degrees, 30.3372 minutes west
Because this data is string data, it's essentially an exercise in cutting the string at specific
points to derive the values you want. Once you have them, the math to convert them to the
more familiar latitude and longitude (if you remember that was WGS84) format is very
simple.
First, you need to separate the first two digits from the latitude string and the first three from
the longitude. This gives us the following:
53
and
21.5802
for the north direction
006
and
30.3372
for west
Because there are 60 minutes in a degree, we must divide the minutes digits by sixty to find
what fraction of a degree they are, and then combine them with our whole degrees. So, for
our latitude:
53
+ (21.5812/60)
will give you
53.359686
degrees.
And for our longitude:
6 + (30.3372/60)
will give you
6.505620
degrees.
You get simple positions from the numbers. To finish the conversion, you need to apply the
north and west directions as positive or negative numbers. The easiest way to manage
which directions are positive or negative is to change any west or south measurements to
negative. So with our numbers, the final coordinates in WGS84 latitude and longitude are:
53.359686, -6.505620
WGS84 is a global coordinate system standard, and while it is widely used, using it for
everything can cause some problems. Because WGS84 is designed to cover the globe, it's
designed also to be very lenient with the curvature of the planet. Think back to the wireframe
globe in Figure 4. Notice the shape of the rectangles as they near the top of the globe.
