How to transform latitude and longitude?

Question

How to calculate from these numbers:

51.501690392607,-0.1263427734375

to latitude and longitude?

It should be London, England 51° 32' N 0° 5' W

Answer 1

http://geography.about.com/library/howto/htdegrees.htm

This seems to work out.

Answer 2

To convert the 51.501690392607, first take the integer portion for 51 degrees. Positive values are north; negatives are south.

Then take the fractional portion: 0.501690392607

Multiply by 60: 60 * 0.501690392607 = 30.10142355642

Take the integer portion for 30 minutes.

Then take the fractional portion: 0.10142355642

Multiply by 60: 6.0854133852

Round to the nearest 1 for the seconds.

You come out with: 51 degrees North 30 minutes 6 seconds.

For the East/West direction, repeat with east positive and west negative.

To find the city, you'll have to use some database or something...

I don't know why your conversion doesn't seem to match up.

Answer 3

The basic conversion between the two representation can be done like this:

// to decimal
decimal = degree + minutes/60 + seconds/3600;

// from decimal
degree = int(decimal)
remaining = decimal - degree
minutes = int(remaining*60)
remaining = remaining - minutes/60
seconds = remaining*3600

Answer 4

To convert a fractional number of degrees into degrees and minutes, in pseudocode:

degrees = int(frac)
minutes = int((frac - degrees) * 60)

to convert "negative" numbers into "S" and "W" (vs "N" and "E") respectively, use "if".

Just to make the pseudocode executable, we could use Python...:

def translate(frac, islatitude):
    if islatitude: decorate = "NS"
    else: decorate = "EW"
    if frac < 0:
        dec = decorate[1]
        frac = abs(frac)
    else:
        dec = decorate[0]
    degrees = int(frac)
    minutes = int((frac - degrees) * 60)
    return "%d %d %s" % (degrees, minutes, dec)

So for example:

print translate(51.501690392607, True),
print translate(-0.126342773437, False)

would emit

51 30 N 0 7 W

The decoration (degrees and minutes signs) depends on the character set support of your output device -- and the 7 vs 5 minutes of arc for the W coordinate seems to be the right result for the input numbers you give.