Converting from UTC to local time
Jonathan
Posts: 1,023
in Propeller 1
HI All,
I have been working on putting a new GPS into an older project. I have a nixie clock that I made in the 90's and then sometime after the Prop1 came out I converted it to a Prop. My old GPS had a setting for UTC offset but the new module does not. Is there a slick way to convert to local time? I am -7 or -8 hours from UTC.
Thanks!
Comments
I can't think of a hard way to do it! It's really easy: just convert the UTC hours to an integer, and add your timezone offset to it. If the result is below zero, add 24 and subtract one from the day. If that result is below one set it to the number of days from the previous month, and subtract one from the month. And if that result is below one, set it to 12, and subtract one from the year.
-Phil
Hi Phil,
Yup, that is what I had come up with. I seem to remember that there was some slick way of doing it. I have been looking around but haven't found it. I also used to have some way of figuring out if it was DST or standard time but I haven't found that yet either. I must have lost some code along the way or I just don't know where to look in my old files.
Many thanks!
You don't mention what language you're using, but if it's C then there are standard library functions for converting between UTC and local time. PropGCC and flexspin have them, Catalina probably does as well.
I am using Spin, I should have mentioned that. I have been meaning to look at flexspin, I will give that a shot,
Thanks!
You could convert it to unix time, make the time zone adjustment, and then convert back to year, month, day, hour, minute and seconds. I have routines written in Spin that do the conversions.
EDIT: I've attached unixtime.spin that contains the routines I mentioned. The routines include a parameter for the timezone offset.
This is my solution as well. It is a bit more complex but it works everywhere, always, and also makes compensating for DST a snap. All you need to know is the TZ offset from UTC in seconds, the date/time DST starts (if DST is observed) and the length DST runs (238 days in the US, if I remember correctly).
If you know you’ll never need to leave the “mainstream” timezones, then Phil’s solution works great for time zones with an integer offset from UTC. But it doesnt work on those “off-by-30-minute” oddballs auch as found in India, Sri Lanka, Afghanistan, Iran, Myanmar, Newfoundland, Regions of Australia, Venezuela, Nepal, Chatham Islands, and the Marquesas Islands. If true “anywhere” compatability is needed, you’ll need to use the more complex method.
@"Dave Hein" Thanks a ton! It will be a week until I am back where the project is. I will try to grok your code between now and then.
@Jonathan
A couple of years ago I wrote in C++/Prop a complete gps parser and have the extra math to change any time and also to do siderial time as I am building a GEM Mount for my telescope from scratch.
If you would like I can send it to you. I also have a book that you may be interested in as it covers celestial time and positions very interesting