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What have we learned about time?

What have we learned about time?. Time Instants and Intervals. Time is continuous but data are discrete At instants of time Over intervals of time Time is indexed by instantaneous time stamps In relational databases, intervals are time stamped at the beginning . Time.

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What have we learned about time?

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  1. What have we learned about time?

  2. Time Instants and Intervals • Time is continuous but data are discrete • At instants of time • Over intervals of time • Time is indexed by instantaneous time stamps • In relational databases, intervals are time stamped at the beginning Time 2010-02-23T10:05:00Z-08:00 = 23 Feb 2010, 10:05 AM, Pacific Standard Time 2010-01-01T00:00:00 = Year 2010, Month Jan 2010, and Day Jan 1, 2010 Time instants can be readily specified …. …. Time intervals are more elusive

  3. “Dimensions” of Time • Begin with hourly data and then average the data: • For each day • For each month • For each year • For a day of the year • For a month of the year • For an hour of the day • 2010-02-23T10:00:00 Parse a time stamp into “dimensions”….. ……. Plot the data for each dimension

  4. Time Zones Prime Meridian in Space (0º) has Universal Coordinated Time (Z) We need spatial-temporal reference frames……. …. and functions for “projecting” data in space-time

  5. Universal Coordinate Time (Greenwich Mean Time) Downward Solar Radiation (W/m2) January 2003 • Universal Coordinate Time (UTC) is like Geographic Coordinates in space • Local Time at any location is offset from UTC • Offset may change seasonally (Daylight and Standard time) 1200 Z GIS should transparently handle time coordinate transformations ……

  6. Conclusions • Time is a subtle thing • Really continuous but data are discrete • Time stamps play a key role • Instantaneous at the beginning of intervals • Time has interacting “dimensions” • Hour, day, month, year • Time has two forms: • Universal time (like geographic coordinates) • Local time (like projected coordinates) • We need space-time reference frames • Tools for moving data between them 2010-02-23T10:05:00Z-08:00 Space Time

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