[aprssig] APRS LAT/LONG standards

Tapio Sokura oh2kku at iki.fi
Sun May 29 11:45:16 EDT 2005

Keith Kotch wrote:
> Would someone please take the time to publish the math formulas for
> converting lat/lon coordinates to and from different formats?  Please give
> examples for each conversion starting with a DD/MM/SS coordinate and use the
> same coordinate throughout the examples.
> DD/MM/SS to DD.MM.mmmm 
> DD/MM/SS to DD.dddd
> And so on...

Here's a decimal degrees format location: N60.052017 E024.504512

To convert to degrees and minutes, multiply the fractional part with 60 
and keep the integer part from the starting location as the degrees value:
0.052017 * 60 = 3.12102, so N60 deg 3.12102 min
0.504512 * 60 = 30.27072, so E024 deg 30.27072 min

To further convert to degrees, minutes and seconds, do the same for minutes:
0.12102 * 60 = 7.2612, so N60 deg 3 min 7.2612 sec
0.27072 * 60 = 16.2432, so E024 deg 30 min 16.2432 sec

 From seconds to minutes and degrees you reverse the process, now divide 
the seconds with 60 and add it to the minutes value:
7.2612 / 60 = 0.12102, so N60 deg 3.12102 min
16.2432 / 60 = 0.27072, so E024 deg 30.27072 min

And again for decimal degrees:
3.12102 / 60 = 0.052017, so N60.052017 deg
30.27072 / 60 = 0.504512, so E024.504512 deg

You can dump the last few decimals from the values shown above in 
practice, here they are kept to illustrate the maths.

So the formula isn't that difficult, but doing it accurately without a 
calculator can be time consuming. I've made a small J2ME MIDP 1.0 
application for cellphones/pdas that converts between the typically used 
coordinate formats in Finland. The part that does d/m/s conversions 
works for anywhere in the world, if you have a suitable phone you can 
give it a go at http://www.oh2kku.ham.fi/ota/ .


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