coordinate systems

Jonathan Gregory (
Thu, 07 Aug 1997 17:35:32 +0100 (BST)

Dear John,

I shall be away after today until Monday 18th - as other people have said, my
silence until then does not indicate a lack of interest. Unfortunately I do not
have time to answer your posting fully. Two comments only:

> More difficult examples are 1) hybrid coords and 2) (generate_time,
> reference_time): are these "values on a single axis"? The hybrid coords
> are really parameters to a function that map level indices to a single
> axis, and (generate_time, reference_time) i think are really two
> different axis.

I agree with that. (1) are components and therefore a single axis; (2) are
different axes.

> I need to think about some of the unresolved issues. How would you
> implement example 11?

Example 11 is the time-components, I believe. For a time-axis, GDT propose
encoding its components into simple numbers, because decomposition can be
done unambiguously. However, if you did want to record the separate components
(year,month,day,hour,minute,second) GDT would put them in as additional 1D
coordinate vectors associated with the main (encoded) vector.

Best wishes,