Re: [LEAPSECS] LEAPSECS Digest, Vol 51, Issue 22

2011-02-07 Thread Richard B. Langley
GPS Time actually come from a "paper clock" composed of all satellite and ground station clocks: . -- Richard Quoting Tony Finch : On Mon, 7 Feb 2011, Steve Allen wrote: Until there is an ensemble of cesium chronometers not on the surface of the earth

Re: [LEAPSECS] LEAPSECS Digest, Vol 51, Issue 22

2011-02-07 Thread Richard B. Langley
Those wishing to "bone up" on geodesy and coordinate systems, especially those used in the U.K., may wish to read: -- Richard Quoting Ian Batten : On 7 Feb 2011, at 17:21, Finkleman, Dave

Re: [LEAPSECS] LEAPSECS Digest, Vol 51, Issue 22

2011-02-07 Thread Warner Losh
On 02/07/2011 11:12, Tony Finch wrote: On Mon, 7 Feb 2011, Steve Allen wrote: Until there is an ensemble of cesium chronometers not on the surface of the earth there is no easy way to measure the potential depth to 1e-10, so the corrections currently being used to compensate for the NIST and PTB

Re: [LEAPSECS] LEAPSECS Digest, Vol 51, Issue 22

2011-02-07 Thread Tony Finch
On Mon, 7 Feb 2011, Steve Allen wrote: > > Until there is an ensemble of cesium chronometers not on the surface of > the earth there is no easy way to measure the potential depth to 1e-10, > so the corrections currently being used to compensate for the NIST and > PTB chronometers being about a mile

Re: [LEAPSECS] LEAPSECS Digest, Vol 51, Issue 22

2011-02-07 Thread Ian Batten
On 7 Feb 2011, at 17:21, Finkleman, Dave wrote: > I finally get a chance to look like I might know something. > > Neiher Gravity nor the Geoid are "standardized." Witness that maps from > some countries do not employ WGS-84. United Kingdom uses OSGB36 rather than WGS84, and a different Elip

Re: [LEAPSECS] LEAPSECS Digest, Vol 51, Issue 22

2011-02-07 Thread Steve Allen
On Mon 2011-02-07T12:21:08 -0500, Finkleman, Dave hath writ: > Neiher Gravity nor the Geoid are "standardized." The SI definition for TAI says "rotating geoid". Resolution B1.9 (Re-definition of Terrestrial Time TT) from the XXIVth IAU GA recognizes both that the geoid changes and that it is hard

Re: [LEAPSECS] LEAPSECS Digest, Vol 51, Issue 22

2011-02-07 Thread Poul-Henning Kamp
In message <3b33e89c51d2de44be2f0c757c656c880a1c4...@mail02.stk.com>, "Finklema n, Dave" writes: >I finally get a chance to look like I might know something. > >Neiher Gravity nor the Geoid are "standardized." Indeed. I was surprised when I tried to confirm my recollection about the TAI/MSL thin

Re: [LEAPSECS] LEAPSECS Digest, Vol 51, Issue 22

2011-02-07 Thread Finkleman, Dave
I finally get a chance to look like I might know something. Neiher Gravity nor the Geoid are "standardized." Witness that maps from some countries do not employ WGS-84. (Korea was this way. I am not sure whether they still are.) There are "best practices" documents, including some issued by st