[tz] Dealing with Pre-1970 Data

[Lester Caine]

Guy Harris wrote:
>> Stephen Colebourne wrote:
>> >
>>> >>Final note. LMT can now be safely ignored in this discussion.
>> >Agreed, although I would make a request for some support in code rather than the database.
> So you'd like the tz code to include a routine that takes, as an argument, a longitude value and a seconds-since-the-Epoch time value, and converts it to LMT (independent, of course, of the current time zone), so that people who want LMT rather than local standardized time for a particular location on Earth would call that routine, supplying it the longitude of that location, rather than calling localtime(), and, similarly, supply a routine that takes a "struct tm" and a longitude value and returns a seconds-since-the-Epoch value, so that people who want to convert an LMT date/time value for a particular location on Earth, rather than a local standardized time date/time value for a particular tzdb zone, to seconds-since-the-Epoch would call that routine, supplying it the longitude for that location, rather than calling mktime()?

That is the simple bit, Longitude to an offset from UTC with an option for a 
15deg zone version, and yes I know it's pig simple, but a function just 
completes the jigsaw. If a search on the database does not return a 'hit', we 
default to an LMT zone (15deg slot), or a simple LMT offset.

However the one I was really thinking about was the 'equation of time' 
calculation in a format we can use as a 'standard'. Not sure Paul will see the 
necessity, but it's one of those 'useful functions' that is very much time 
related. The main problem here is that accuracy of results are going to depend 
on the compiler/language used so there is not going to be a 'definitive' answer?

These are more related to pre-1970 activity, so many people are probably not 
interested, but I am sure there is a 'demand' for a reference set of material 
for this aspect of time?

-- 
Lester Caine - G8HFL
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