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Re: FAA To Finally Ditch Floppy Disks & Win-95

From rbowman <bowman@montana.com>
Newsgroups comp.os.linux.misc
Subject Re: FAA To Finally Ditch Floppy Disks & Win-95
Date 2025-06-23 05:35 +0000
Message-ID <mbs7dgFbafcU2@mid.individual.net> (permalink)
References (20 earlier) <8judncOVBsnUxsr1nZ2dnZfqnPSdnZ2d@giganews.com> <mbpla6Ft9taU1@mid.individual.net> <FCV5Q.1598985$G6Lf.181139@fx17.iad> <mbr2nlF5ijfU2@mid.individual.net> <DZ_5Q.1372755$6%s6.27132@fx12.iad>

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On Sun, 22 Jun 2025 21:55:47 GMT, Charlie Gibbs wrote:

> I've written call accounting software for local 911 centres. The
> switches give us latitude and longitude in degrees with six decimals. 
> That narrows it down to about 4 inches, which seems a bit optimistic,
> unless you somehow have access to a differential GPS setup.  

Back in the bad old days of K&E slide rules, even with magnifying cursors, 
you learned to do some sanity checking. Six decimal accuracy with consumer 
grade GPS receivers that have 5 to 10 meter accuracy on the best of days 
doesn't pass the sanity check. 

As AVL systems in the equipment became more prevalent we'd get a variety 
of formats, NMEA sentences being a popular one. 

https://w3.cs.jmu.edu/bernstdh/web/common/help/nmea-sentences.php

Most of the USB hockey puck receivers spit them out and we'd wait for a 
GGA or RMC sentence. 

Years ago Trimble was a big player when emergency services started using 
AVL and they had their own format. Geocom, another player, sent the 
coordinated in hex. It's been a long time but there was also a magic 
number involved where x and y were the hex values.

	*lat = (double) x * 5.729577957 * .0000001;
	*lon = (double) y * 5.729577957 * .0000001;

CalAmp sends a very proprietary struct with the values packed in big 
endian format.  Great fun.

Anyway, it all ended up as decimal degrees. Th job wasn't finished since 
most of the GIS data was in State Plane Coordinate System. 

https://en.wikipedia.org/wiki/State_Plane_Coordinate_System

Like the article say, having Cartesian coordinates makes the math a lot 
easier. With spherical coordinates to find the distance from A to B you 
need to use the haversine or Vincenty's  formula. 

https://en.wikipedia.org/wiki/Vincenty's_formulae

Six decimal places in a double might imply accuracy that isn't really 
there, but you definitely don't want to try to cram it into a float and 
expect a happy ending when you start your conversions.


> A friend
> who calibrated aeronautical navaids before he retired told me how they'd
> set up a differential GPS transmitter at an airport and get 1-centimeter
> accuracy while flying an approach.
> (Worst-case WAAS is 20 feet vertically, less horizontally - competitive
> with ILS.)

With DGPS, RTK, and post processing you can get the accuracy down to 
millimeters. 

I have a Amzfit Active 2 fitness watch that has a pretty good GPS. I'm 
amused by the posters on reddit complaining that they took an out and back 
hike and the two tracks aren't exactly on top of each other or doesn't 
show them on the sidewalk. They expect miracles from a $100 consumer 
device with a minimal patch antenna and also put a lot of trust in digital 
maps. 

I started using a GPS back in the '90s before Clinton took selective 
availability off. Even then it was a revelation. I was used to dealing 
with Forest Service maps of dubious accuracy and the notorious Forest 
Service miles that were even worse. It was amusing that what I had 
identified as Dead Skunk Point based on a crappy map and not knowing 
exactly where I was really wasn't Dead Skunk Point.

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Thread

FAA To Finally Ditch Floppy Disks & Win-95 c186282 <c186282@nnada.net> - 2025-06-13 22:38 -0400
  Re: FAA To Finally Ditch Floppy Disks & Win-95 rbowman <bowman@montana.com> - 2025-06-14 03:35 +0000
    Re: FAA To Finally Ditch Floppy Disks & Win-95 c186282 <c186282@nnada.net> - 2025-06-14 00:29 -0400
      Re: FAA To Finally Ditch Floppy Disks & Win-95 Rich <rich@example.invalid> - 2025-06-14 16:34 +0000
        Re: FAA To Finally Ditch Floppy Disks & Win-95 The Natural Philosopher <tnp@invalid.invalid> - 2025-06-15 00:38 +0100
          Re: FAA To Finally Ditch Floppy Disks & Win-95 c186282 <c186282@nnada.net> - 2025-06-14 23:28 -0400
            Re: FAA To Finally Ditch Floppy Disks & Win-95 Rich <rich@example.invalid> - 2025-06-15 14:04 +0000
              Re: FAA To Finally Ditch Floppy Disks & Win-95 c186282 <c186282@nnada.net> - 2025-06-15 21:44 -0400
        Re: FAA To Finally Ditch Floppy Disks & Win-95 c186282 <c186282@nnada.net> - 2025-06-14 22:41 -0400
          Re: FAA To Finally Ditch Floppy Disks & Win-95 Rich <rich@example.invalid> - 2025-06-15 14:19 +0000
            Re: FAA To Finally Ditch Floppy Disks & Win-95 rbowman <bowman@montana.com> - 2025-06-15 18:45 +0000
            Re: FAA To Finally Ditch Floppy Disks & Win-95 c186282 <c186282@nnada.net> - 2025-06-15 22:02 -0400
              Re: FAA To Finally Ditch Floppy Disks & Win-95 Rich <rich@example.invalid> - 2025-06-16 03:00 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 c186282 <c186282@nnada.net> - 2025-06-16 01:13 -0400
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Rich <rich@example.invalid> - 2025-06-17 03:42 +0000
              Re: FAA To Finally Ditch Floppy Disks & Win-95 Charlie Gibbs <cgibbs@kltpzyxm.invalid> - 2025-06-16 17:52 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Rich <rich@example.invalid> - 2025-06-17 03:49 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 c186282 <c186282@nnada.net> - 2025-06-17 01:29 -0400
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Charlie Gibbs <cgibbs@kltpzyxm.invalid> - 2025-06-17 18:20 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 c186282 <c186282@nnada.net> - 2025-06-17 23:06 -0400
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Rich <rich@example.invalid> - 2025-06-18 14:15 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 c186282 <c186282@nnada.net> - 2025-06-18 19:38 -0400
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Lawrence D'Oliveiro <ldo@nz.invalid> - 2025-06-18 00:02 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Bobbie Sellers <bliss-sf4ever@dslextreme.com> - 2025-06-17 17:30 -0700
                Re: FAA To Finally Ditch Floppy Disks & Win-95 c186282 <c186282@nnada.net> - 2025-06-17 22:38 -0400
                Re: FAA To Finally Ditch Floppy Disks & Win-95 rbowman <bowman@montana.com> - 2025-06-18 03:55 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 John Ames <commodorejohn@gmail.com> - 2025-06-18 08:03 -0700
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Charlie Gibbs <cgibbs@kltpzyxm.invalid> - 2025-06-18 16:15 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 c186282 <c186282@nnada.net> - 2025-06-18 19:41 -0400
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Charlie Gibbs <cgibbs@kltpzyxm.invalid> - 2025-06-19 22:25 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Lawrence D'Oliveiro <ldo@nz.invalid> - 2025-06-19 23:12 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Chris Ahlstrom <OFeem1987@teleworm.us> - 2025-06-20 08:36 -0400
                Re: FAA To Finally Ditch Floppy Disks & Win-95 rbowman <bowman@montana.com> - 2025-06-20 20:00 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 c186282 <c186282@nnada.net> - 2025-06-21 01:34 -0400
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Chris Ahlstrom <OFeem1987@teleworm.us> - 2025-06-21 06:50 -0400
                Re: FAA To Finally Ditch Floppy Disks & Win-95 rbowman <bowman@montana.com> - 2025-06-21 19:30 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Chris Ahlstrom <OFeem1987@teleworm.us> - 2025-06-22 06:43 -0400
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Charlie Gibbs <cgibbs@kltpzyxm.invalid> - 2025-06-21 23:57 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 rbowman <bowman@montana.com> - 2025-06-22 01:15 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 c186282 <c186282@nnada.net> - 2025-06-21 21:24 -0400
                Re: FAA To Finally Ditch Floppy Disks & Win-95 rbowman <bowman@montana.com> - 2025-06-22 06:14 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 c186282 <c186282@nnada.net> - 2025-06-22 02:50 -0400
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Charlie Gibbs <cgibbs@kltpzyxm.invalid> - 2025-06-22 15:49 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 rbowman <bowman@montana.com> - 2025-06-22 18:22 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 c186282 <c186282@nnada.net> - 2025-06-23 00:40 -0400
                Re: FAA To Finally Ditch Floppy Disks & Win-95 John Ames <commodorejohn@gmail.com> - 2025-06-23 11:27 -0700
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Lawrence D'Oliveiro <ldo@nz.invalid> - 2025-06-24 01:34 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 John Ames <commodorejohn@gmail.com> - 2025-06-24 07:52 -0700
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Lawrence D'Oliveiro <ldo@nz.invalid> - 2025-06-24 22:24 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 John Ames <commodorejohn@gmail.com> - 2025-06-25 09:20 -0700
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Lawrence D'Oliveiro <ldo@nz.invalid> - 2025-06-26 03:36 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Andreas Eder <a_eder_muc@web.de> - 2025-06-29 15:20 +0200
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Lawrence D'Oliveiro <ldo@nz.invalid> - 2025-06-30 00:01 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 rbowman <bowman@montana.com> - 2025-06-23 18:43 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 The Natural Philosopher <tnp@invalid.invalid> - 2025-06-22 11:43 +0100
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Charlie Gibbs <cgibbs@kltpzyxm.invalid> - 2025-06-22 15:49 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 c186282 <c186282@nnada.net> - 2025-06-23 01:01 -0400
                Re: FAA To Finally Ditch Floppy Disks & Win-95 rbowman <bowman@montana.com> - 2025-06-23 18:46 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Charlie Gibbs <cgibbs@kltpzyxm.invalid> - 2025-06-24 04:52 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 rbowman <bowman@montana.com> - 2025-06-24 05:06 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 c186282 <c186282@nnada.net> - 2025-06-24 01:24 -0400
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Lawrence D'Oliveiro <ldo@nz.invalid> - 2025-06-24 06:31 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 The Natural Philosopher <tnp@invalid.invalid> - 2025-06-24 10:19 +0100
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Lawrence D'Oliveiro <ldo@nz.invalid> - 2025-06-24 22:25 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 rbowman <bowman@montana.com> - 2025-06-25 02:02 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 c186282 <c186282@nnada.net> - 2025-06-25 01:58 -0400
                Re: FAA To Finally Ditch Floppy Disks & Win-95 c186282 <c186282@nnada.net> - 2025-06-25 02:17 -0400
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Charlie Gibbs <cgibbs@kltpzyxm.invalid> - 2025-06-22 15:49 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 rbowman <bowman@montana.com> - 2025-06-22 19:09 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Charlie Gibbs <cgibbs@kltpzyxm.invalid> - 2025-06-22 21:55 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Lawrence D'Oliveiro <ldo@nz.invalid> - 2025-06-23 02:25 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 c186282 <c186282@nnada.net> - 2025-06-23 01:07 -0400
                Re: FAA To Finally Ditch Floppy Disks & Win-95 rbowman <bowman@montana.com> - 2025-06-23 05:52 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 rbowman <bowman@montana.com> - 2025-06-23 05:35 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Charlie Gibbs <cgibbs@kltpzyxm.invalid> - 2025-06-23 16:43 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 rbowman <bowman@montana.com> - 2025-06-23 19:11 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Lawrence D'Oliveiro <ldo@nz.invalid> - 2025-06-24 01:36 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Charlie Gibbs <cgibbs@kltpzyxm.invalid> - 2025-06-24 04:52 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Lawrence D'Oliveiro <ldo@nz.invalid> - 2025-06-24 06:47 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 c186282 <c186282@nnada.net> - 2025-06-24 01:02 -0400
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Chris Ahlstrom <OFeem1987@teleworm.us> - 2025-06-22 06:49 -0400
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Charlie Gibbs <cgibbs@kltpzyxm.invalid> - 2025-06-22 15:49 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 c186282 <c186282@nnada.net> - 2025-06-22 02:14 -0400
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Lawrence D'Oliveiro <ldo@nz.invalid> - 2025-06-18 22:44 +0000
          Re: FAA To Finally Ditch Floppy Disks & Win-95 rbowman <bowman@montana.com> - 2025-06-15 18:36 +0000
            Re: FAA To Finally Ditch Floppy Disks & Win-95 c186282 <c186282@nnada.net> - 2025-06-15 22:40 -0400
              Re: FAA To Finally Ditch Floppy Disks & Win-95 rbowman <bowman@montana.com> - 2025-06-16 04:11 +0000
                Re: FAA To Finally Ditch Floppy Disks & Win-95 c186282 <c186282@nnada.net> - 2025-06-16 01:30 -0400
                Re: FAA To Finally Ditch Floppy Disks & Win-95 Charlie Gibbs <cgibbs@kltpzyxm.invalid> - 2025-06-16 18:15 +0000
      Re: FAA To Finally Ditch Floppy Disks & Win-95 John Ames <commodorejohn@gmail.com> - 2025-06-16 09:35 -0700
        Re: FAA To Finally Ditch Floppy Disks & Win-95 Rich <rich@example.invalid> - 2025-06-17 04:00 +0000
          Re: FAA To Finally Ditch Floppy Disks & Win-95 c186282 <c186282@nnada.net> - 2025-06-17 04:22 -0400
        Re: FAA To Finally Ditch Floppy Disks & Win-95 c186282 <c186282@nnada.net> - 2025-06-17 23:11 -0400
          Re: FAA To Finally Ditch Floppy Disks & Win-95 John Ames <commodorejohn@gmail.com> - 2025-06-18 08:01 -0700

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