#168: Addition of grid mapping for radar and lidar data in radial coordinates
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Reporter: mikedixon | Owner: cf-conventions@…
Type: enhancement | Status: new
Priority: medium | Milestone:
Component: cf-conventions | Version:
Resolution: | Keywords: radar lidar grid mapping
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Comment (by jonathan):
Dear Mike
OK. Thanks for explaining. In that case I agree that it makes sense to add
it as a grid mapping. Please could you draft it in the same form as the
other entries in Appendix F, and write out the additions to the table of
attributes at the end of Appendix F? When we make a change to the
convention, we have to agree exactly what text changes are needed, so that
implementing them is purely editorial.
I guess you may have used the attribute names referring to "projection
origin" because they already existed. However, I wonder whether these are
really the clearest words you could use, since this isn't really a map
projection. Am I right in thinking that these specify the location of the
instrument? Also, "height" could be confusing, because that's a CF
standard name which means height above the ''surface''. If you want height
above the geoid (almost the same as mean sea level) it would be better to
use "altitude", which is the standard name for that quantity.
You say there's a standard algorithm for doing the conversion. That's
good, and it would therefore help to say what it is and give a reference
for it in the Appendix F entry. Are there any other possible algorithms
which might be used? If so, you could have another attribute to identify
how the conversion would be done.
For the auxiliary coordinates, is it the case that they would be time-
dependent? If they were independent of time, they could be provided once,
in a separate file - we could add a mechanism for that. But that won't
work if they're different for every data file. In that case, I think we
would need to change the start of section 5.6, if you can't require
auxiliary coordinates, since it says, "When the coordinate variables for a
horizontal grid are not longitude and latitude, it is required that the
true latitude and longitude coordinates be supplied via the `coordinates`
attribute." For example, you could add another sentence, such as "For
radial (polar) coordinate variables for radar and lidar data, it is
optional to provide latitude, longitude and vertical coordinates via the
`coordinates` attribute, and recommended if practicable." I think it
should be encouraged at least, since it makes the data more user-friendly.
Best wishes
Jonathan
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Ticket URL: <https://cf-trac.llnl.gov/trac/ticket/168#comment:11>
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