[LINK] Ffx: 'Farmers ‘crippled’ ... as GPS-guided tractors grind to a halt'

[Roger Clarke]

Ah, the Link Institute scores again.

>> On 19 Apr 2023, at 5:20 pm, Kim Holburn <kim at holburn.net> wrote: >> I haven't read all this yet but how could this all possibly depend 
on just one satellite?  One satellite would only be above the horizon 
for half of the time.  How would that even work?>> When I look at GNSS 
satellites ATM I see 80 at any one time.  That includes US GPS, Chinese 
BDS, Russian Glonass, European Galileo, Indian IRNSS/Navic, Japanese QZSS.
On 19/4/23 5:45 pm, Carl Makin wrote:
> The satellite that went down was in geostationary orbit.  It was providing GPS correction signals for not only Geoscience’s SBAS open pilot, but for proprietary correction systems from Trimble and others across the whole asia/pacific region (along with other stuff like aircraft voice and data coverage over the ocean).
> 
> The GPS receivers use GPS, Galileo, Glonass LEO satellites etc for the primary location signal which is accurate to about 10m, then the corrections from the Inmarsat satellite to refine that fix down to, in this case, less than 10cm.

The reporter dramatised this bit, but mis-phrased it, resulting in at 
least Roger mis-reading what had happened:
 > Tractors ... are enabled with GPS tracking and can be guided to an 
accuracy within two centimetres  ...  All that went out the window when 
the Inmarsat-41 satellite signal failed.

So "all that" is misleading, and would be better as 'they lost the 
refinement from +/10m [?] to +/- <10cm (and maybe even +/- 2cm?)'.


-- 
Roger Clarke                            mailto:Roger.Clarke at xamax.com.au
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Visiting Professor in the Faculty of Law            University of N.S.W.
Visiting Professor in Computer Science    Australian National University