
The data is a sequence of raw images (frames).  They are have an associated
time and world coordinates.  Combining them into a 3-d array gives a data
structure with spatial coordinates along axes and a third temporal axis.

Any 2-d slice of this data (a timeseries) will have a time axis and a space
axis.  I want an object that keeps this metadata with the raw data.

A Field is a subclass of an numpy.ndarray that includes dimensional
information.  Slices can be made along the indices and the dimensions
automatically calculated in the returned object. Alternatively, world
coordinates can be given and the indices are computed internally.


