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Friday, 20 July 2018

Working with Coordinates

Working with Coordinates

Displaying/Writing
Degrees         °   
Minutes         ’
Seconds        ”
Feet               ‘
Inches           “

Standardised Distances for Degrees, Decimal Degrees, Minutes and Seconds

                     N Mile        Metres
  1°               = 60             111,120
  0.5°            = 30               55,560
  0.1°            = 06               11,112

 30’               = 30                 55,560
  1’                = 1                     1,852    
  0.1’             = 0.1                     185.2    
  0.01’           = 0.01                     18.52        
  0.001’         = 0.001                     1.852

  1.0”         = 0.01666666667              30.86
  0.5”        = 0.008333333333             15.43
  0.1”        = 0.001666666667             03.08

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Coordinates
Below is the same position displayed 3 ways?

Degrees Decimal Degrees
DDD.DDDDDDD°
23.55500° S    150.5551333° E

Degrees Minutes and Decimal Minutes
DDD° MM.MMM'
23° 33.300' S    150° 33.308' E

Degrees Minutes Seconds and Decimal Seconds
DDD MM SS.S
23° 33' 18.00" S    150° 33' 18.48" E
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Here is how to convert from Degrees Decimal Degrees to Degrees Minutes and Seconds.

There is 60 minutes in a degree
To find the minutes in the decimal of a degree, multiply the decimal of a degree by 60

For an example using the latitude
23.55500° S

.55500° x 60 = 33.3’

The answer in degrees minutes and decimal minutes
23° 33.300'

There is 60 seconds in a minute
To find the seconds in the decimal of a minute, multiply the decimal of a minute by 60

.300' x 60 = 18.00"

The answer in degrees minutes seconds and decimal seconds
23° 33' 18.00"

Work through the longitude to prove it for yourself
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If you want to check you can work it through, go to Google Maps and move the location of Google Maps to the marina finger or to the mooring your boat is located at, then click on that position, the little pop up box will give you the location in degrees decimal degrees (DDD.DDDDDD) of that point.  You should have pretty good idea of your vessels location, now convert the degrees decimal degrees into DDD MM.MMM and/or DDD MM SS.SS and see if it matches the location of your chart plotter/hand held (don’t forget to allow for antenna offset if you’re on a super yacht).
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Want to work it the other way, convert: Degrees Minutes Seconds and Decimal Seconds to Degrees Decimal Degrees.

Degrees Minutes Seconds
23° 33' 18.00" S

This time divide only the seconds by 60

18.00" / 60 = .300'

The answer in Degrees Minutes and Decimal Minutes
23° 33.300' S

Next time divide the Minutes by 60
33.300' / 60 = .555°

The final answer in Degrees Decimal Degrees is

DDD.DDDDDDD°
   23.5550000° S

As a quick mental cross check remember 15 minutes is .25 of a degree, 30 minutes is .50 of a degree and 45 minutes is .75 of a degree.  

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