[aprssig] APRS LAT/LONG standards

Tapio Sokura oh2kku at iki.fi
Thu May 26 19:27:02 EDT 2005

Robert Bruninga wrote:
> And the use of seconds is totally obsolete...

DMS format is commonly used in civil aviation, at least on this side of 
the pond.

I wrote a reply message after reading the first post on this topic by 
Bob, but pressed cancel because I didn't want to start another thread 
going around and around on the same arguments. Now that a couple of 
rounds have already been taken I guess my input won't stir it up that 
much anymore.

In my opinion decimal degrees, counting time with seconds from a UTC 
epoch etc similar continuous systems are good in protocols and computers 
in general, simply because they are easy to handle and are efficient in 
terms of storage space and calculation. It should always be the job of 
the user interface to seamlessly convert the data to the format the user 
wants it and back to the internal format again. I personally prefer 
degrees and minutes because that's what I'm used to and I have developed 
some mental mapping on what the DM coordinates are in certain places.

As has been pointed out, you can't avoid doing conversions when you have 
a map that has a UTM or a national grid system and the coordinates you 
have are geographical, for example. In Finland most terrestrial (other 
than air/sea) maps are in a coordinate system/datum that is not used 
anywhere else in the world. Some maps have geographical coordinates, but 
usually they are not in WGS-84, although the difference is only about 
100 meters.

What Curt said about coordinates said over the air or casually scribbled 
by a non-surveyor on a piece of paper is very true and I have personally 
observed these things happening many times. I tend to prefer grid 
coordinates when said over the air because there is no confusion between 
degrees/mintes/seconds and also northing and easting can be easily 
recognized from the figure itself. But the typical SAR team member 
(here) is a Red Cross first aid volunteer and doesn't know much about 
datums and such so it is not uncommon to have to guesstimate what format 
the numbers we get are given are in.

So the problem is really not just D vs. DM vs. DMS but all coordinate 
systems used on a given area. When people from different fields that 
traditionally use differing coordinate systems come together, you need 
to do conversions. The only possible way around this is for all to use a 
common system, but that is not going to happen. Maybe 20 years into the 
future we only have one datum/ellipsoid in common use in Finland, but 
even then there will probably be at least grid and geographical 
coordinates in use. And the geographical ones will probably still be 
d/dm/dms depeding on who is using them..


More information about the aprssig mailing list