Hi Jim,
One other thing to think on is the set of 'rate' Standard Names, or are you happy with my prefix from the yaw example added on to your definitions.
And finally are we intending to propose platform_sway and platform_surge as new Standard Names in addition to platform_heave which started this discussion even though nobody has specifically asked for them?
Cheers, Roy.
I have now retired but will continue to be active through an Emeritus Fellowship using this e-mail address.
________________________________
From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> on behalf of Jim Biard <jbiard at cicsnc.org>
Sent: 06 August 2018 16:47
To: CF Metadata List; Jonathan Gregory
Subject: Re: [CF-metadata] Platform Heave
Hi.
There are other standard names that call for a separate attribute or variable that provides context. The attributes (at the moment) are all standard CF attributes (cell_methods, flag_meanings, comment, etc). I'd love to get feedback from the community about whether or not a directionality attribute would need to described as a "standard" CF attribute.
I'll be glad to rework the definitions to make them directionality-agnostic when I get back next week.
Grace and peace,
Jim
[CICS-NC]<
http://www.cicsnc.org/>Visit us on
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http://ncdc.noaa.gov/>
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On Sat, Aug 4, 2018 at 3:45 AM Lowry, Roy K. <rkl at bodc.ac.uk<mailto:rkl at bodc.ac.uk>> wrote:
Dear Nan,
So are we returning to the wording in Alison's original definitions (e.g. yaw normally clockwise facing front) before you with my support asked for the ambiguity be removed? Or do you want to go even further with no mention of sign convention at all?
I would also question whether a Standard Name definition is the place to specify the mechanism to be used for the description of a sign convention as it has wider implications than the parameters currently under discussion. Would it not be more appropriate for this to be considered an enhancement to CF and written into the Conventions document? If so, it should it not be the subject of a GitHub ticket?
Cheers, Roy.
I have now retired but will continue to be active through an Emeritus Fellowship using this e-mail address.
________________________________
From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu<mailto:cf-metadata-bounces at cgd.ucar.edu>> on behalf of Nan Galbraith <ngalbraith at whoi.edu<mailto:ngalbraith at whoi.edu>>
Sent: 04 August 2018 02:18
To: cf-metadata at cgd.ucar.edu<mailto:cf-metadata at cgd.ucar.edu>
Subject: Re: [CF-metadata] Platform Heave
Thanks, Jim.
> change the definitions to avoid declaring which direction is
> positive, make the direction attribute optional, and say that users
> should be careful about assuming the directionality for variables
> lacking the attribute.
This is the approach I'd prefer as well.
- Nan
Quoting Jim Biard <jbiard at cicsnc.org<mailto:jbiard at cicsnc.org>>:
> Nan,
>
> I didn't go to the lengths of making new regularized definitions
> before I wrote that list. I was thinking in terms of making the
> clockwise/anticlockwise call based on the right hand rule and the
> unit vector for each axis. For roll, for example, if the X unit
> vector faces forward, the "right side down" roll is actually
> anticlockwise - that is, it is in the direction that your right hand
> fingers curl if you grab the unit vector in your hand with your
> thumb pointing in the same direction as the unit vector. That
> definition is independent of observer location and look direction.
> My definitions for all the direction values are following that same
> convention.
>
> Accurate knowledge of the sign of roll, pitch, and yaw is critical
> in the satellite and aircraft world. The look angles for remote
> sensors are affected by these values. I get it that not all systems
> care about the signed values, so that reason and for backward
> compatibility I suggested that we could change the definitions to
> avoid declaring which direction is positive, make the direction
> attribute optional, and say that users should be careful about
> assuming the directionality for variables lacking the attribute.
>
> Grace and peace,
>
> Jim
>>
>> On 8/3/18 2:03 PM, Nan Galbraith wrote:
>>> Hi Roy -
>>>
>>> Yes, I've been looking at that page quite a bit lately, and I
>>> think it backs up
>>> what I'm saying.
>>>
>>> If you are standing on that fuselage (may we never), facing
>>> forward, the red roll
>>> arrow is showing a clockwise motion, with right side moving
>>> downward. If you
>>> were facing aft, the arrow would be anticlockwise, but the right side would
>>> be rising.
>>>
>>> So, 'roll: "clockwise" for positive right side up and
>>> "anticlockwise" for positive right
>>> side down' - is backwards in either case. I'm not disputing
>>> anything except
>>> the term 'clockwise' in this phrase.
>>>
>>> Thanks - Nan
>>>
>>> On 8/3/18 1:43 PM, Lowry, Roy K. wrote:
>>>>
>>>> Hi Nan,
>>>>
>>>>
>>>> Whilst I appreciate the limitations of Wikipedia as an
>>>> authoritative source have a look at
>>>> https://en.wikipedia.org/wiki/Aircraft_principal_axes
[
https://upload.wikimedia.org/wikipedia/commons/thumb/5/54/Flight_dynamics_with_text.png/1200px-Flight_dynamics_with_text.png]<
https://en.wikipedia.org/wiki/Aircraft_principal_axes>
Aircraft principal axes - Wikipedia<
https://en.wikipedia.org/wiki/Aircraft_principal_axes>
en.wikipedia.org<
http://en.wikipedia.org>
Normal axis, or yaw axis ? an axis drawn from top to bottom, and perpendicular to the other two axes.Parallel to the fuselage station.; Transverse axis, lateral axis, or pitch axis ? an axis running from the pilot's left to right in piloted aircraft, and parallel to the wings of a winged aircraft.
>>>>
>>>>
>>>> Cheers, Roy.
>>>>
>>>>
>>>> ------------------------------------------------------------------------
>>>> *From:* Nan Galbraith <ngalbraith at whoi.edu<mailto:ngalbraith at whoi.edu>>
>>>> *Sent:* 03 August 2018 18:23
>>>> *To:* Jim Biard; Lowry, Roy K.; kkehoe at ou.edu<mailto:kkehoe at ou.edu>
>>>> *Subject:* Re: [CF-metadata] Platform Heave (pitch, roll)
>>>> Hi Jim, Roy and Ken -
>>>>
>>>> I'm skipping the list because this is a minor point and ... and I may be
>>>> missing
>>>> something obvious.
>>>>
>>>> It's hard not to think of these terms as they apply to ships. In that
>>>> environment,
>>>> we'd use the convention of the observer facing forward; therefore roll
>>>> would be
>>>> clockwise if the right side were going down, not up. I'm supposing that
>>>> would
>>>> also apply to aircraft.
>>>>
>>>> Cheers - Nan
>>>>
>>>>
>>>>
>>>>> If we declare that X is positive forward, that Y is positive left,
>>>>> that Z is positive up, and that we use the right-hand rule for angle
>>>>> directions, the direction attribute values could be:
>>>>>
>>>>> * roll: "clockwise" for positive right side up and "anticlockwise"
>>>>> for positive right side down.
>>>>> * pitch: "clockwise" for positive nose up and "anticlockwise" for
>>>>> positive nose down.
>>>>> * yaw: "clockwise" for positive nose right and "anticlockwise" for
>>>>> positive nose left.
>>>>> * surge: "positive" for positive forward and "negative" for
>>>>> positive backward.
>>>>> * sway: "positive" for positive left and "negative" for positive right.
>>>>> * heave: "positive" for positive up and "negative" for positive down.
>>>>>
>>>>
>>>>
>>>>>
>>>>>>>
>>>>>>> ------------------------------------------------------------------------
>>>>>>> >>>
>>>>>>> *From:* CF-metadata <cf-metadata-bounces at cgd.ucar.edu<mailto:cf-metadata-bounces at cgd.ucar.edu>> on behalf of
>>>>>>> Jim Biard <jbiard at cicsnc.org<mailto:jbiard at cicsnc.org>>
>>>>>>> *Sent:* 03 August 2018 15:41
>>>>>>> *To:* cf-metadata at cgd.ucar.edu<mailto:cf-metadata at cgd.ucar.edu>
>>>>>>> *Subject:* Re: [CF-metadata] Platform Heave
>>>>>>>
>>>>>>> I freely admit that I picked direction on sway arbitrarily. In my
>>>>>>> experience, part of the variation that arises in the definitions of
>>>>>>> the different motions arises from different thoughts about their
>>>>>>> use, particularly whether someone is thinking the values are used to
>>>>>>> transform into the platform body frame vs transform from it. Or
>>>>>>> maybe they just aren't worrying about consistency. Like as not,
>>>>>>> choices have often been made in attempts to make the values have the
>>>>>>> signed-ness that felt right to people, and we can't keep to
>>>>>>> conventions like the right hand rule and make it all work
>>>>>>> consistently. We want a positive pitch to be nose up. We want a
>>>>>>> positive yaw to be nose right. We want positive heave to be up. My
>>>>>>> natural tendency is to think of "roll right" as positive and "sway
>>>>>>> right" as positive, but that isn't what other people think of.
>>>>>>>
>>>>>>> As I read what I wrote, I realize I didn't use a consistent approach
>>>>>>> to position and look direction when assigning clockwise and
>>>>>>> anticlockwise to roll, pitch, and yaw. I need to regularize that.
>>>>>>>
>>>>>>> Reading the Conventions about vertical coordinates, it says they
>>>>>>> must all have a "positive" attribute with a value of "up" or "down".
>>>>>>> I don't see a problem with having the definitions back off of
>>>>>>> declaring a specific directionality and add an attribute declaring
>>>>>>> directionality. We could call the attribute "direction" so as not to
>>>>>>> step on the "positive" attribute, and say that if the attribute is
>>>>>>> not present that the user should not assume which direction is correct.
>>>>>>>
>>>>>>> If we declare that X is positive forward, that Y is positive left,
>>>>>>> that Z is positive up, and that we use the right-hand rule for angle
>>>>>>> directions, the direction attribute values could be:
>>>>>>>
>>>>>>> * roll: "clockwise" for positive right side up and "anticlockwise"
>>>>>>> for positive right side down.
>>>>>>> * pitch: "clockwise" for positive nose up and "anticlockwise" for
>>>>>>> positive nose down.
>>>>>>> * yaw: "clockwise" for positive nose right and "anticlockwise" for
>>>>>>> positive nose left.
>>>>>>> * surge: "positive" for positive forward and "negative" for
>>>>>>> positive backward.
>>>>>>> * sway: "positive" for positive left and "negative" for positive
>>>>>>> right.
>>>>>>> * heave: "positive" for positive up and "negative" for positive down.
>>>>>>>
>>>>>>> Thoughts?
>>>>>>>
>>>>>>> BTW, I'll be out until August 13.
>>>>>>>
>>>>>>> Grace and peace,
>>>>>>>
>>>>>>> Jim
>>>>>>>
>>>
>>>
>>
>> --
>> CICS-NC <http://www.cicsnc.org/> Visit us on
>> Facebook <http://www.facebook.com/cicsnc> *Jim Biard*
>> *Research Scholar*
>> Cooperative Institute for Climate and Satellites NC <http://cicsnc.org/>
>> North Carolina State University <http://ncsu.edu/>
>> NOAA National Centers for Environmental Information <http://ncdc.noaa.gov/>
>> /formerly NOAA?s National Climatic Data Center/
>> 151 Patton Ave, Asheville, NC 28801
>> e: jbiard at cicsnc.org<mailto:jbiard at cicsnc.org> <mailto:jbiard at cicsnc.org>
>> o: +1 828 271 4900
>>
>> /Connect with us on Facebook for climate
>> <https://www.facebook.com/NOAANCEIclimate> and ocean and geophysics
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>> us on Twitter at _at_NOAANCEIclimate
>> <https://twitter.com/NOAANCEIclimate> and _at_NOAANCEIocngeo
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>>
>>
>
> --
> CICS-NC <http://www.cicsnc.org/> Visit us on
> Facebook <http://www.facebook.com/cicsnc> *Jim Biard*
> *Research Scholar*
> Cooperative Institute for Climate and Satellites NC <http://cicsnc.org/>
> North Carolina State University <http://ncsu.edu/>
> NOAA National Centers for Environmental Information <http://ncdc.noaa.gov/>
> /formerly NOAA?s National Climatic Data Center/
> 151 Patton Ave, Asheville, NC 28801
> e: jbiard at cicsnc.org<mailto:jbiard at cicsnc.org> <mailto:jbiard at cicsnc.org>
> o: +1 828 271 4900
>
> /Connect with us on Facebook for climate
> <https://www.facebook.com/NOAANCEIclimate> and ocean and geophysics
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