[aprssig] APRStt for SAR using UTM grid!

[Tom Russo]

On Mon, Jun 17, 2013 at 02:24:42PM -0400, we recorded a bogon-computron collision of the <bruninga at usna.edu> flavor, containing:
> We need to resolve this.  I was told by some SAR folks that for all voice
> reporting during a SAR mission, that the XXX,YYY resolution was for the
> 10km square grid with resolution to 10 meters for the purpose of generally
> knowing where everyone was.  Additional digits were only used if higher
> resolution or a different area was of interest.
> 
> Are you saying that not all groups use this convention?

The standard UTM truncation is to keep the 10km, 1km, and 100m digits of the
easting and northing to construct a 6-digit truncated coordinate.  The 8 digit 
coordinate keeps 10km, 1km, 100m, and 10m.  This is pretty much universal, and 
is what is done in USNG and MGRS.

Any group using any other truncation is just making up their own thing.

Look on any USGS topo map at the format of the UTM tick marks they provide.
The grids on these maps are 1000m grids.  You'll find that they are labeled
with a small digit (or two small digits) followed by larger digits.  The
small digits are the ones dropped for the truncated forms of UTM coordinates
(including USNG and MGRS), leaving a 2-digit identifier for the 1000m grid.
A third digit is added for constructing UTM coordinates at 100m precision.

> -----Original Message-----
> From: aprssig-bounces at tapr.org [mailto:aprssig-bounces at tapr.org] On Behalf
> Of Tom Hayward
> Sent: Monday, June 17, 2013 10:48 AM
> To: TAPR APRS Mailing List
> Subject: Re: [aprssig] APRStt for SAR using UTM grid!
> 
> On Sun, Jun 16, 2013 at 6:22 AM, John Langner WB2OSZ <wb2osz at comcast.net>
> wrote:
> > Here is another APRStt implementation which includes processing of UTM
> > coordinates.
> >
> > http://home.comcast.net/~wb2osz/Version%200.7/APRStt-Implementation-No
> > tes.pd
> > f
> >
> > DTMF decoding is done in software so no special hardware is required.
> 
> This is a good start, but you've implemented a non-standard UTM truncation
> system:
> 
> > The xxx and yyy ranges would extend over a 10 x 10 km area with 10 meter
> resolution.
> 
> Typical UTM truncation (as in the MGRS and USNG spec) is an order of
> magnitude higher, so xxxyyy extends over a 100km x 100km area with 100
> meter resolution. To add resolution, add a 10m digit to give you xxxxyyyy
> format.
> 
> Tom KD7LXL
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-- 
Tom Russo    KM5VY   SAR502   DM64ux          http://www.swcp.com/~russo/
Tijeras, NM  QRPL#1592 K2#398  SOC#236        http://kevan.org/brain.cgi?DDTNM
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