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Understanding Time: Instants, Intervals, and Dimensions in Space-Time

Explore the concepts of time instants, intervals, and dimensions in space-time, including how time is continuous but data are discrete. Learn about time stamps, time zones, and coordinate transformations.

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Understanding Time: Instants, Intervals, and Dimensions in Space-Time

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Presentation Transcript

  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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