Re: Problems with GLONASS Raw Receiver Data at Start of New Year
On Jan 14, 2006, at 8:59 AM, Richard Langley wrote: The problem existed for only 2-1/2 minutes, not hours. Thanks for the clarification. Might be coincidental with the leap second but I've not noticed this problem at other times. Would be a significant coincidence. Any simple explanation for the 90 second lag in the issue being triggered? The latency associated with emergent behavior is of interest in itself. Stations were not running during the previous leap second. Right - that's a central fact influencing policy. That different groups take this to imply that different choices should be made adds a little spice to the discussion :-) UNB1 Web page is here: http://gge.unb.ca/Resources/UNB1.html. IGS Central Bureau Web page is here: http://igscb.jpl.nasa.gov/ Thanks for the pointers. Rob Seaman NOAO
Re: The real problem with leap seconds
On Fri 2006/01/13 14:20:21 -, Michael Deckers wrote in a message to: LEAPSECS@ROM.USNO.NAVY.MIL Then why can the IERS express UTC in the MJD notation? Good point. The only such usage I am aware of is in IERS Bulletin A where the MJD column is given without saying even whether it's UTC, TAI, UT1, or something else. In fact, in the situation where it's used the accuracy doesn't warrant it. Mark Calabretta ATNF
Re: The real problem with leap seconds
On Fri 2006/01/13 11:45:13 -, Ed Davies wrote in a message to: LEAPSECS@ROM.USNO.NAVY.MIL If you don't count the leap seconds then the good news is that days are all 86 400 seconds long but the bad news is that the real is undefined during the leap second and there's a discontinuity (or rather, a surprising continuity in that at some point it's 23:59:59.99 and a whole second and a tiny bit later it's 00:00:00.). Agreed. I would add that two occasions when you would do this is in computing UT1 and time_t. The use of the 23:59:60 notation is described in ISO 8601. Is it also specified in TF.460? If so, how do they relate it to the notion of DTAI? In practice, refer to the example I gave on Jan/12. Mark Calabretta ATNF
Re: The real problem with leap seconds
On Fri 2006/01/13 16:45:33 -, Michael Deckers wrote in a message to: LEAPSECS@ROM.USNO.NAVY.MIL Right, UTC timestamps are ambiguous (in the sense that the ... would have been ambiguous ... corresponding TAI value is not known) in the vicinity of positive leap seconds, and the notation with a second field = 60 s is one (elegant) way to disambiguate. ... had not the variable-radix notation not been introduced. Another way to disambiguate is to record the value of DTAI together with a UTC (or TAI) timestamp. Such a method is standardised in ISO 8601 for denoting offsets from UTC, but only with minute resolution. I seem to remember that Clive Feather once proposed this for an extension to the C programming language. ... where UTC here is taken to be in the usual (fixed-radix) sexagesimal format. Mark Calabretta ATNF
Re: Monsters from the id
On Fri 2006/01/13 18:39:01 CDT, John Cowan wrote in a message to: LEAPSECS@ROM.USNO.NAVY.MIL The situation with the proposed leap hour is quite different. Given that AEST is defined as UTC+1000, and AEDT as UTC+1100, would someone care to speculate, in terms similar to the above, what will happen when a leap hour is inserted? Perhaps the two scales will be labeled O.S. and N.S., as our anglophone antecessors did when switching from Julian to Gregorian. If you go through the exercise trying to tie leap hours to DST, as I challenged, you will discover that it raises many questions that are not addressed by the leap hour proposal. If you make some plausible assumptions as to how it would operate, with DST starting and ending at the usual times of year and leap hours occurring on new year's eve, I believe you will find it far from simple to do in a rigorous fashion, and that at least one of the timescales is genuinely discontinuous. Mark Calabretta ATNF
Re: Monsters from the id
Mark Calabretta scripsit: If you go through the exercise trying to tie leap hours to DST, as I challenged, you will discover that it raises many questions that are not addressed by the leap hour proposal. I realize the ALHP has severe problems with this, but I don't approve of the ALHP anyhow (save perhaps tactically, as explained). If you make some plausible assumptions as to how it would operate, with DST starting and ending at the usual times of year and leap hours occurring on new year's eve, I believe you will find it far from simple to do in a rigorous fashion, and that at least one of the timescales is genuinely discontinuous. Indeed. But the sensible approach would be for each State government to fail to omit the hour of the normal spring transition in the year 2700, say. In that way, AEDT would become TI+1000 and a normal-looking autumn transition would cause AEST to become TI+0900. Countries without DST transitions would have to actually repeat an hour, of course, just as Algeria had to do in 1940, 1956, 1977, and 1981 (the country has repeatedly flipflopped between UTC+ and UTC+0100). By the way, I re-counted all the secular time zone transitions worldwide. According to the Olson timezone database, there have been 516 of them since the beginning of standard time (when that is, of course, varies with the country or subdivision thereof). -- John Cowan http://www.ccil.org/~cowan [EMAIL PROTECTED] Be yourself. Especially do not feign a working knowledge of RDF where no such knowledge exists. Neither be cynical about RELAX NG; for in the face of all aridity and disenchantment in the world of markup, James Clark is as perennial as the grass. --DeXiderata, Sean McGrath
