Time zones and daylight saving time

In general, mixing data from multiple time zones and different daylight saving time rules can cause a great deal of complexity. For this reason, normalize the data if you're working with different time zones and daylight saving time rules by converting all the time stamps to a single time zone and daylight saving time rule set. Coordinated Universal Time (UTC) is a good choice for normalizing data across time zones.

If you are unable to normalize your data using a single time zone, ArcGIS provides functionality to translate times from one time zone to another. Each TimeInstant or TimeExtent has a TimeReference object associated with it. TimeReference includes all the time zone and daylight saving time information. TimeReference is conceptually similar to a spatial reference. You can use it to project a time object from one time zone to another time zone. You can also associate one of several predefined time zones with a given time object.

For example, if you're collecting information about bird migratory patterns and have data collected from Global Positioning System (GPS) tracking devices, this data is probably stored in Greenwich Mean Time (GMT). To compare this data to local temperature readings, sunrise/sunset times, and other local data, you can translate the GMT values to a local time zone by using the project function of the TimeReference object. Simply get the TimeReference of the local data, and pass it to the project function of the GMT values. This translates the time value from GMT to the local time zone.

This process also works for mixing values that use daylight saving time with values that ignore daylight saving time. If your GMT values ignore daylight saving time, but your local data has a TimeReference that uses daylight saving time, the process described in this topic will translate the GMT values ahead or behind (as appropriate) for the local daylight saving time rules.