Hello Jonathan,
Looking back, I see that I actually started this platform thread, so I suppose I should try to push it along...
I agree with omitting platform_longitude, platform_latitude, and the "true" and "indicated" designators.
I agree with including:
platform_speed_wrt_ground ("ground speed") (m s-1)
platform_speed_wrt_air ("air speed") (m s-1)
platform_speed_wrt_sea_water ("water speed") (m s-1)
platform_pitch_angle (degree)
platform_roll_angle (degree)
platform_pitch_rate (degree s-1)
platform_roll_rate (degree s-1)
platform_orientation ("pointing direction") (degree)
platform_course ("travel direction") (degree)
The one case I can think of a yaw variable being useful and measurable is in the case of towfish, in which yaw is typically defined as the difference between orientation and course. I imagine there may be other similar useful situations, so I'd support adding the variables:
platform_yaw ("difference between orientation and course")(degree),
platform_yaw_rate (degree s-1)
So do we also want:
platform_orientation_rate (degree s-1)
platform_course_rate (degree s-1)
Also you asked:
>Is it usual to speak of ship ground speed i.e. relative to the solid
>Earth, even though no ground is evident?
The absolute ship speed variable that I am used to seeing is given as "SOG", which stands for "Speed Over Ground", so I'd have to say yes, it is usual.
Regards,
Mike
-----Original Message-----
From: cf-metadata-bounces at cgd.ucar.edu [mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf Of Jonathan Gregory
Sent: Sunday, September 11, 2005 12:33 AM
To: cf-metadata at cgd.ucar.edu
Subject: [CF-metadata] platform standard names
Dear all
> all variables regarding the platform are prefaced with 'platform_'
I agree that "platform" is a useful generic name for something moving from which observations are made.
We are discussing standard names for quantities which are properties of the platform, such as its velocity. This is different from existing standard names, which describe observable properties of the world and say nothing about the observer or the method of observation. The platform_ standard names are providing information which is useful for interpreting or correcting the measurements, I presume. In a sense it is metadata rather than data, since once the appropriate corrections have been made and the data from different sources assembled into some dataset that could be used as a climatology, for example, there is no further need for the information about the platform.
> latitude, longitude and altitude are not appropriately prefaced.
I don't think we need platform_ versions of these since they are coordinates.
Practically, if we did introduce platform_latitude, I don't think people would use it consistently instead of latitude.
> Jonathans earlier confusion where he didn't even realize [I think]
> that true_air_speed was that of the aircraft and not the wind.
Since I wasn't certain, I was suggesting that "ground speed" and "air speed", although commonly used terms, do not have completely obvious meanings. Hence I propose standard names of:
platform_speed_wrt_ground ("ground speed") (m s-1) platform_speed_wrt_air ("air speed") (m s-1) platform_speed_wrt_sea_water ("water speed") (m s-1)
Is it usual to speak of ship ground speed i.e. relative to the solid Earth, even though no ground is evident?
I *don't* think we should have separate standard names for indicated and true air speed if these are the same quantity with and without some correction.
While the speed of the platform is an observable quantity which some other observer could measure, corrections of various kinds relate to instruments and methods of measurement, and we could get into huge complexity if we try to include that kind of metadata in standard names, I fear. Another attribute should be used to characterise corrections, such as long_name or comment.
Similarly, we need
platform_pitch_angle (degree)
platform_roll_angle (degree)
What about yaw (the third axis)?
> There is also potential for platform_pitch_rate...
platform_pitch_rate (degree s-1)
platform_roll_rate (degree s-1)
> Is there anything wrong with using platform_heading ... and platform_course?
The problem with "heading" is that it means direction of travel as well as the direction you're pointing in. That's what I understood it to mean when Michael proposed it, and why I asked if it was the same thing as course.
Looking on Google, I find that half the definitions are direction of travel.
Hence "heading" is too confusing, I'd say. How about
platform_orientation (degree) for the direction the platform is pointing in platform_course (degree) for the direction it's travelling in?
Again, I don't think we should have names for "true" heading, quantities with and without correction for magnetic declination, etc.
Best wishes
Jonathan
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Received on Thu Sep 29 2005 - 15:49:04 BST
