Spatial is Special, what about Time?

pocket knife
The swiss are known for clocks and pocket knives, so why didn’t they include a watch on this pocket knife?

If you’ve worked much with GIS there’s a good chance you’ve had to go through the why-spatial-is-special routine with a DBA wanting to store geometry as numeric columns within normalized tables.

But what about time?

Say you’re using GPS clock to compute location via time difference of arrival (TDOA). Nanosecond precision is needed (speed of light = 1 foot per nanosecond), however, SQL Server doesn’t support anything finer than 3.33 microseconds. This could be overcome by introducing a time column with an ITemporalReference. Internally it would store time as a 64bit integer along with a domain and scale – just like with spatial types. ITime is to IGeometry what ITemporalReference is to ISpatialReference. A simpler (though perhaps more confusing) alternative might be to overload the M (measure) value of geometry to allow time to be stored as a measure.

On the other end of the scale is geologic time, which falls outside the .NET DateTime structure limits. In this case the domain would be much larger.

From the helpdoc:

What is the best way for storing temporal data – a netCDF file or a relational database? Which one is faster?

Storing temporal data in relational database is just as viable as using a netCDF file. ESRI’s support of netCDF is primarily to support the existing community of netCDF data and users, not to force people to learn about a new file format. The decision should be made based on how you want to create and manage data in your organization.

It looks like netCDF addresses this issue. But what if I don’t want to represent time using netCDF or date columns as ESRI suggests?


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