Re: DTM sentence and Russian datums in US phones (yes, that's clickbait!)

[Greg Troxel]

"Gary E. Miller" <gem@rellim.com> writes:

>>   inexplicable buggy behavior in choice of or reprorting of datum,
>> which has not been shown to cause a perceptible error
>
> Buggy I buy, but very explixable.

What is inexplicable is:

  Why does a cellphone with a US-designed chipset, sold in the US for US
  use, by default provide positions labeled as being in a Russian datum?

>> They never do but I don't think that has anything to do with assuming
>> frame equivalnce when merging multiple constellations.
>
> No assumptions needed.  All constellations use Earth Centered Inertial
> coordinates derived from Kepler parameters.  Those are all converted to
> ECEF so they can all be used in computing one solution.  Only after an
> ECEF solution is computed is that transformed to a datum.

ECEF just means XYZ.  One still needs a datum label for origin,
orientation and scale.

>> >> What's funny is that PZ90.11 is so close to ITRF2008 that unless
>> >> you are playing at the 10 cm level or better it can be treated ~=
>> >> ITF2008 != WGS84(G1762).  
>> >
>> > And what about the other WGS84 that are > 10 cm from WGS84(G1762).  
>> 
>> It's only the older ones that are that far off (TRANSIT and G730),

> I suggest you look at the USGS error maps for the PNW.  > 10 cm.

I have not seem the USGS deal in WGS84 at all.

What I meant is that transforms between any two WGS84(x) and WGS84(y), x
 > G730, y > G730, are very small and not detectable with a
non-differential solution.

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