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
Cheers, Roy.
------------------------------------------------------------------------
*From:* Nan Galbraith <ngalbra...@whoi.edu>
*Sent:* 03 August 2018 18:23
*To:* Jim Biard; Lowry, Roy K.; kke...@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-boun...@cgd.ucar.edu> on behalf of
>>> Jim Biard <jbi...@cicsnc.org>
>>> *Sent:* 03 August 2018 15:41
>>> *To:* cf-metadata@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
>>>
