In message: <[EMAIL PROTECTED]>
"Tom Van Baak" <[EMAIL PROTECTED]> writes:
: Too much is made of the "overflow". Fields rollover all
: the time in real life and it's often a simple engineering
: matter to take this into account. Not sure I would call
: it "cheating". We get by fine with just 7 names for days
: of the week; calendars that rollover every 12 months,
: wristwatches that overflow every 12 hours...
These instances of overflow come from remainders of division
operations overflowing. They all can be derived from a single base
number (say number of seconds since 1970, MJD, etc). However, when
you are deriving that single base number, it can be much harder.
Could you tell me what year it was if I told you it was Monday,
October 15th? No, you couldn't. You could tell me that it might be
2001, but it could also be 2007 or 1990. You need more information to
resolve the ambiguity. If I told you that it was Monday, October 15th
and that TAI-UTC=32, you'd know it was 2001. If I told you
TAI-UTC=100, you might guess that it is 2063, or maybe even 2068 or
2057 or maybe other years earlier or later depending on your leap
second model, utc-ut1 tolerance parameters, and other factors
unknowable today.
The GPS 1024 week overflow is easier to deal with, since it is a 20
year ambiguity, not a 5 year one. You can make a better guess than in
my example, I'll not argue. The better the guess you make based on
today's understanding, the more external factors that might cause you
to be wrong. Eg, leap second rules changes, lifetime of GPS signals,
etc.
I guess I agree with you that these things are doable. Working out
the details, however, makes them non-trivial.
Warner
