[CF-metadata] Conventions for Unstructured Grid Data

From: Jonathan Gregory <j.m.gregory>
Date: Mon, 15 Nov 2004 22:08:04 +0000

Dear Tom

I think we didn't finish the earlier discussion, back in February.

We need to have standard names for the various quantities that define your
mesh, such as your "Horizontal Triangular Element Incidence List" and "Boundary
Segment Node List". We agreed that the convention for whether it numbers from
0 or 1 needs to be stated. You've suggested doing this with the units
attribute e.g. units="index_start_1". I think that it would be better to put
the "start 0" or "start 1" information into the standard name itself because

(a) units="index_start_1" or similar is not a legal udunit. Hence it would
cause a problem to anything which uses udunits to interpret the attribute.

(b) we do not use units to indicate sign conventions, and this strikes me as
a similar kind of issue.

(c) it is absolutely essential that this information is specified. With
physical quantities you could often make an intelligent guess if the units
weren't specified, but in this case a guess would be hard to make. Since it is
essential, putting it in the standard name is good because it's unavoidable.

However a compromise might be to consider putting this into a standard_name_
parameter which has to be specified as well as the standard name, such as we
have been discussing in another thread.

Any comments?

Best wishes

Jonathan
Received on Mon Nov 15 2004 - 15:08:04 GMT