[aprssig] APRS LAT/LONG standards

Curt, WE7U archer at eskimo.com
Thu May 26 13:22:29 EDT 2005

On Thu, 26 May 2005, Robert Bruninga wrote:

> One problem noted in the after-action summary was
> the problem of converting between GPS coordinates
> from Decimal degrees to DEGREES and MINUTES.
> This is exactly why the APRS standard for GPS
> coordinates in HAM radio was supposed to be the
> GPS standard of DEG and decimal MINUTES.  So
> that we wouldn't always have to be doing conversions.
> Some of the follow-on APRS clones did not follow
> this standard and this strong advice and simply
> used the convenient programmers format of
> decimal degreees because that is how they do
> computations.   When I complained that this is
> NOT used by ANY human system of navigation
> and that it will only lead to frustration by the users,
> the response was "Oh, they can click on it and
> bring up a menu and convert to any format
> they want".

Decimal degrees _is_ used in a human system of navigation.  Aircraft
use it.

If you're attributing that last comment to me I hope it's not what
you took away from our previous discussions on the matter.  See

> ARGH...
> This is OK, but it is furstrating to always have
> to do conversions when the OBJECTIVE and GOAL
> of APRS was to have a standard for human-to
> human tactical information interchange and that
> inclludes the human-to-human echange of
> LAT/LONGS and that is why the APRS standard
> was chosen to match the GPS standard of
> DEG and MINUTES to avoid conversions.
> Please, lets get everyone trained to use
> DEG and decimal minutes in all HAM radio.

This is a subject that is near and dear to my heart.  We end up
having to do multiple conversions on some SAR missions because:

1) Civilian aircraft still use decimal degrees, including our SAR

2) Our county's SAR had gone to a standard of UTM & WGS84,

3) Other counties that assist us have their own standards, sometimes
they have no standards at all,

4) The military uses MGRS, but they can also use decimal degrees in
most (but not all) of their helos in order to coordinate with
civilian airfields,

5) Coordinates coming in from other individuals, including the
subjects at times, can and do come in any format.  Sometimes we get
no specified format at all, just a list of numbers.

Sometimes we lose comms with the person reporting the numbers,
they're not sure how to work their GPS, or we get the numbers from a
third-party with no way to ask questions of the originator of the

I've seen each of these things happen while I was at the search base
doing mapping and/or comms.  I've seen strange things reported in
UTM coordinates as well, but the problem has been much less with
that format and why we've standardized on it in our county's SAR.  I
also use UTM when bowhunting as it is the absolute best coordinate
system for land navigation over shorter distances.

#5 is the reason I wrote a script that will output all permutations
for a set of input coordinates.  Sometimes I need to plot an object
at all three lat/long possibilities in order to figure out which one
or two of them might be reasonable.  One or more permutations are
usually outside our known search area and can be thrown out.

Multiply the above five instances with datum shifts due to known or
unknown datums.  The problem set gets bigger.  Fortunately for SAR
uses in our country it's mostly NAD27 to WGS84 shifts.  It's about a
90 to 105 meter shift depending on where you are in our particular
county so it's not as big of a deal for what we do in most cases.
That datum shift of course changes based on where you are in the

I don't see any of these requirements for other coordinate systems
going away in the near future.

Xastir can be put into any of the below coordinate systems, very
useful during searches:

1) decimal degrees
2) degrees, decimal minutes (APRS standard)
3) degrees, minutes, decimal seconds
4) UTM
5) UTM w/special zones (odd-sized NATO zones, Europe and North)

So... My position is that we need all of these coordinate systems in
order to save lives out in the field.  I won't restrict the Xastir
APRS client to one coordinate system for this reason.  There's more
to navigation than APRS.  A lot more.

    "Search and Rescue:  That others may live."

Curt, WE7U.   APRS Client Comparisons: http://www.eskimo.com/~archer
"Lotto:    A tax on people who are bad at math." -- unknown
"Windows:  Microsoft's tax on computer illiterates." -- WE7U
"The world DOES revolve around me:  I picked the coordinate system!"

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