Temporal offset
The temporal offset feature in Tracking Analyst allows you to display the events in a tracking layer using times that are offset from the times when the events were recorded. Applying a temporal offset to a tracking layer does not affect the date and time information stored in its source data. It only affects how Tracking Analyst displays the data, allowing you to view the data as if it were happening at a different time.
Why do you want to use a temporal offset?
Temporal offsets can be useful for a variety of reasons, but two common uses deserve special mention: side-by-side data analysis and mission planning.
Imagine that you have data from two different time periods that you would like to compare side-by-side. It might be useful to play the two sets of data back as if they were happening at the same time. This would allow you to look for similar patterns or differences in the datasets. For example, you could compare the hurricane seasons for two consecutive years by applying a temporal offset of exactly one year to the data from the first season. Then you could play back the two hurricane seasons together as if they were happening in the same year. This allows you to look for patterns of when and where hurricanes are occurring between the two years. This example is illustrated below:
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In addition to viewing the two hurricane seasons side-by-side on the map, the histogram in the Playback Manager allows you to compare the temporal distributions for the different hurricane seasons. The offset tracking data is shown in a different color so that you can easily compare the different distributions of data. The color used to show offset data can be changed.
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The same concepts can be applied to other situations where side-by-side data analysis would be helpful. For example, you could compare the delivery routes taken by a truck driver for different weeks, or compare the traffic flow in a city for a holiday versus a working day. You could even evaluate the success of a police drill by creating artificial data that represents perfect execution of the drill, and then comparing it to the actual data collected while running the drill.
Another common use of the temporal offset is for mission planning. A mission commander might create several different planned scenarios for time-sensitive troop and vehicle movements using an arbitrary time frame. When the need arises for the actual execution of one of the scenarios, the commander can use a temporal offset to make the planned scenario happen at the current time.
Different ways to apply a temporal offset
A temporal offset can be applied to a tracking layer in two different ways. You can either specify a new start date for the tracking layer or enter a duration for the offset. For the mission-planning scenario described above, entering a new start date would probably be the most convenient way to apply a temporal offset. The commander would set the start date and time for the planned scenario equal to the current date and time. However, for a side-by-side comparison of hurricane data from two consecutive years, it would be easier to simply enter a duration of exactly one year to offset the data for the first year. When setting a temporal offset using a duration, you must specify whether the offset is moving your data into the past or the future.
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Whenever applying temporal offsets, it is important to remember that you may need to adjust the playback window in the Playback Manager to include the offset data. If you offset your data into the future, you may need to change the end time before changing the start time, because the Playback Manager does not allow you to enter a start time that is later than the end time.