iphone - Figure out time by latitude/longitude?

Question

Here's the deal. I have a latitude/longitude set of a location. I need to figure out what the current time is in that location. Here's how I was getting it before:

NSDateFormatter *theFormatter = [[NSDateFormatter alloc] init];
[theFormatter setDateFormat:@"h:mm a"];
NSDate *todaysdate = [NSDate date];
NSString *todaysDate = [theFormatter stringFromDate:todaysdate];
[theFormatter release];

However, I realized that this will give the time for the user's current location. Is there an API somewhere that gives me the time based off of a lat/lon pair?

Thanks in advance.

Answer 1

Unfortunately timezones (and time in general) is never as simple as you would like.

For a simple approximation you can follow jer's suggestion. Longitude ranges from -180 to 180 degrees, there are 24 hours in a day, so you get 15 degrees of longitude per time zone. Center those time zones on 0 degrees longitude so UTC extends from -7.5 to 7.5, UTC+1 is from 7.5 to 22.5, UTC-1 is from -7.5 to -22.5, and so on. You would then have a very simplistic, and wrong, model of how we use time zones.

Take a look at this map of time zones.

• Time zones are not well ordered; regions in UTC-1 are adjacent to regions in UTC-3.
• UTC-9.5, UTC-4.5, UTC+3.5, UTC+5.75, and UTC+13 are all valid time zones and actively in use.

Once you get that sorted out then you can start to consider daylight savings time.