[AstroPy] Convert GPS time to UTC time
aldcroft at head.cfa.harvard.edu
Mon Dec 9 18:37:38 EST 2013
Based on the discussion here I added an astropy issue to consider adding a
GPS time scale:
On Mon, Dec 9, 2013 at 3:58 PM, Paul Hirst <phirst at gemini.edu> wrote:
> On 9/12/13, 09:48 , "Aldcroft, Thomas" <aldcroft at head.cfa.harvard.edu>
> On Mon, Dec 9, 2013 at 12:22 PM, David Berry <d.berry at jach.hawaii.edu>wrote:
>> On 9 December 2013 16:57, Aldcroft, Thomas
>> <aldcroft at head.cfa.harvard.edu> wrote:
>> > This basically creates a Time object with the GPS format
>> representation. By
>> > default this object is in TAI scale, so you first convert to UTC and
>> > ask for the ISO format representation. As I understand GPS is not a
>> > scale, but a simple difference of time in the TAI scale from the given
>> > epoch.
>> Doesn't that make it a timescale? After all TT (Terrestrial Time) is
>> also just a constant offset from TAI.
> This is a good question and one for which I'm definitely interested in
> From what I can see there are two ways to view "GPS time":
> 1. As a time scale which is behind TAI by 19 seconds.
> 2. As a time format which is the floating point number giving the number
> of TAI seconds since UTC 1980-01-06 00:00:00. This is roughly similar to
> the "unix" format or "cxcsec" format.
> I would have thought (1) was actually a more appropriate representation.
> I'm not sure of the formal definition, but I always considered GPS time to
> be another timescale, which just happens to have a nice and simple
> transformation to and from TAI - I understand it's by definition just the
> simple and exact 19.0 second offset.
> Depending on the level of accuracy required, I don't think that's true
> for TT as suggested above, the TT = TAI - 32.184s is an approximation; a
> more accurate transformation is given at eg
> Now, I'm not suggesting that this is a priority for implementation right
> now, but in general I'm thinking that having things as separate time scales
> would make it easier in the future for someone to contribute a more
> advanced transformation - as opposed to figuring out how to make it a
> separate timescale first.
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