I'm OK with that.
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On Wed, Aug 29, 2018 at 3:54 PM Ethan Davis <edavis at ucar.edu> wrote:
> Hey Jim,
>
> How about removing one layer of terminology by using your definitions for
> the allowed values of "direction":
>
> roll: "positive_right_side_up" and "positive_right_side_down".
> pitch: "positive_nose_up" and "positive_nose_down".
> yaw: "positive_nose_right" and "positive_nose_left".
> surge: "positive_forward" and "positive_backward".
> sway: "positive_left" and "positive_right".
> heave: "positive_up" and "positive_down".
>
> Cheers,
>
> Ethan
>
> On Wed, Aug 29, 2018 at 12:02 PM Jim Biard <jbiard at cicsnc.org> wrote:
>
>> John,
>>
>> There are a variety of conventions for defining roll, pitch, and yaw out
>> there. This is why we are avoiding a specific one. Others have searched
>> existing datasets that are using earlier versions of these standard names
>> (or not using standard names) and found that they don't all follow the same
>> convention.
>>
>> Ethan,
>>
>> We purposely aren't answering that question directly because of the issue
>> above. I believe that I have consistently followed the convention in which
>> clockwise and anticlockwise are rotational directions around a unit vector
>> facing the observer, where the X unit vector is in the nominally forward
>> direction, the Z axis is in the local up direction, and the Y axis unit
>> vector is "Z cross X", which forms a right-handed coordinate system. The
>> terms are meaningful and accurate using that convention, but the names
>> could be "alpha" and "beta" or "dog" and "cat" as long as they are used
>> correctly.
>>
>> This whole topic is fraught with competing conventions, so we are
>> attempting to avoid declaring that only one of them is valid, with it's
>> corresponding requirement that everyone follow that one sign convention.
>>
>> In fact, we could reword things to remove naming the axes X, Y, and Z,
>> and perhaps we should. I know of satellite platforms that define their Y
>> axis unit vector as pointing forward and the Z axis unit vector as pointing
>> down.
>>
>> Thoughts?
>>
>> Grace and peace,
>>
>> Jim
>>
>> On 8/29/18 1:32 PM, John Helly wrote:
>>
>> Perhaps one should refer to the discipline of hydrostatics for help with
>> this? This paper, pulled from a quick search, has a diagram referencing
>> the platforms' frame of reference with respect to its center of gravity.
>> Sorry if this comment is retrograde.
>>
>> https://www.hindawi.com/journals/mpe/2010/934714/
>>
>> J.
>>
>> On 8/29/18 10:09, Ethan Davis wrote:
>>
>> Hi Jim, all,
>>
>> I'm a bit confused by the "clockwise" and "anticlockwise". You mention
>> the orientation of the observer but not the location/orientation of the
>> clock. My assumptions (not sure why) for the clock: for roll, the observer
>> (who is facing forward) would be facing the clock; for pitch, the observer
>> would look right to see the clock; and for yaw, the observer would look
>> down to see the clock. That works for your definitions of pitch and yaw,
>> but is backwards for roll.
>>
>> Does "clockwise" add, in some way, another degree of freedom to the
>> definition? Does that degree of freedom need to be nailed down in the
>> definitions? Or other terms used instead? I don't have any good suggestions
>> other than "positive" and "negative".
>>
>> Cheers,
>>
>> Ethan
>>
>> On Wed, Aug 29, 2018 at 9:03 AM Jim Biard <jbiard at cicsnc.org> wrote:
>>
>>> Hi.
>>>
>>>
>>> I've finally gotten back to this topic! The definitions below call out
>>> an attribute named "direction" that is used to specify the direction for
>>> positive values of the different quantities. We may need to add a
>>> definition for the attribute to the Conventions. The values and meanings
>>> for the direction attribute are:
>>>
>>> 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.
>>>
>>> And here are the standard name definitions:
>>>
>>> platform_roll: Platform is a structure or vehicle that serves as a base
>>> for mounting sensors. Platforms include, but are not limited to,
>>> satellites, aeroplanes, ships, buoys, ground stations, and masts. Roll is a
>>> rotation about an axis (the X axis) that is perpendicular to the local
>>> vertical axis (the Z axis) and is coplanar with the nominal forward motion
>>> direction of the platform. Roll is relative to the ?at rest? rotation of
>>> the platform with respect to the X axis. The ?at rest? rotation of the
>>> platform may change over time. The direction for positive values of roll is
>>> specified by an attribute named direction. The value of the direction
>>> attribute is "clockwise" if positive values of roll represent the right
>>> side of the platform rising as viewed by an observer on top of the platform
>>> facing forward. The value of the direction attribute is "anticlockwise" if
>>> positive values of roll represent the right side of the platform falling.
>>> The directionality of roll values is unspecified if no direction attribute
>>> is present.
>>>
>>> platform_pitch: Platform is a structure or vehicle that serves as a base
>>> for mounting sensors. Platforms include, but are not limited to,
>>> satellites, aeroplanes, ships, buoys, ground stations, and masts. Pitch is
>>> a rotation about an axis (the Y axis) that is perpendicular to both the
>>> local vertical axis (the Z axis) and the nominal forward motion direction
>>> of the platform. Pitch is relative to the ?at rest? rotation of the
>>> platform with respect to the Y axis. The ?at rest? rotation of the platform
>>> may change over time. The direction for positive values of pitch is
>>> specified by an attribute named direction. The value of the direction
>>> attribute is "clockwise" if positive values of pitch represent the front of
>>> the platform rising as viewed by an observer on top of the platform facing
>>> forward. The value of the direction attribute is "anticlockwise" if
>>> positive values of pitch represent the front of the platform falling. The
>>> directionality of pitch values is unspecified if no direction attribute is
>>> present.
>>>
>>> platform_yaw: Platform is a structure or vehicle that serves as a base
>>> for mounting sensors. Platforms include, but are not limited to,
>>> satellites, aeroplanes, ships, buoys, ground stations, and masts. Yaw is a
>>> rotation about the local vertical axis (the Z axis). Yaw is relative to the
>>> ?at rest? rotation of the platform with respect to the Z axis. The ?at
>>> rest? rotation of the platform may change over time. The direction for
>>> positive values of yaw is specified by an attribute named direction. The
>>> value of the direction attribute is "clockwise" if positive values of yaw
>>> represent the front of the platform moving to the right as viewed by an
>>> observer on top of the platform facing forward. The value of the direction
>>> attribute is "anticlockwise" if positive values of yaw represent the front
>>> of the platform moving to the left. The directionality of yaw values is
>>> unspecified if no direction attribute is present.
>>>
>>> platform_surge: Platform is a structure or vehicle that serves as a base
>>> for mounting sensors. Platforms include, but are not limited to,
>>> satellites, aeroplanes, ships, buoys, ground stations, and masts. Surge is
>>> a displacement along an axis (the X axis) that is perpendicular to the
>>> local vertical axis (the Z axis) and is coplanar with the nominal forward
>>> motion direction of the platform. Surge is relative to the ?at rest?
>>> position of the platform with respect to the X axis. The ?at rest? position
>>> of the platform may change over time. The direction for positive values of
>>> surge is specified by an attribute named direction. The value of the
>>> direction attribute is "positive" if positive values of surge represent the
>>> platform moving forward as viewed by an observer on top of the platform
>>> facing forward. The value of the direction attribute is "negative" if
>>> positive values of surge represent the platform moving backward. The
>>> directionality of surge values is unspecified if no direction attribute is
>>> present.
>>>
>>> platform_sway: Platform is a structure or vehicle that serves as a base
>>> for mounting sensors. Platforms include, but are not limited to,
>>> satellites, aeroplanes, ships, buoys, ground stations, and masts. Sway is a
>>> displacement along an axis (the Y axis) that is perpendicular to both the
>>> local vertical axis (the Z axis) and the nominal forward motion direction
>>> of the platform. Sway is relative to the ?at rest? position of the platform
>>> with respect to the Y axis. The ?at rest? position of the platform may
>>> change over time. The direction for positive values of sway is specified
>>> by an attribute named direction. The value of the direction attribute is
>>> "positive" if positive values of sway represent the platform moving left as
>>> viewed by an observer on top of the platform facing forward. The value of
>>> the direction attribute is "negative" if positive values of sway represent
>>> the platform moving right. The directionality of sway values is unspecified
>>> if no direction attribute is present.
>>>
>>> platform_heave: Platform is a structure or vehicle that serves as a base
>>> for mounting sensors. Platforms include, but are not limited to,
>>> satellites, aeroplanes, ships, buoys, ground stations, and masts. Heave is
>>> a displacement along the local vertical axis (the Z axis). Heave is
>>> relative to the ?at rest? position of the platform with respect to the Z
>>> axis. The ?at rest? position of the platform may change over time. The
>>> direction for positive values of heave is specified by an attribute named
>>> direction. The value of the direction attribute is "positive" if positive
>>> values of heave represent the platform moving up as viewed by an observer
>>> on top of the platform facing forward. The value of the direction attribute
>>> is "negative" if positive values of heave represent the platform moving
>>> down. The directionality of heave values is unspecified if no direction
>>> attribute is present.
>>>
>>> platform_course: Platform is a structure or vehicle that serves as a
>>> base for mounting sensors. Platforms include, but are not limited to,
>>> satellites, aeroplanes, ships, buoys, ground stations, and masts. Course is
>>> the clockwise angle with respect to North of the nominal forward motion
>>> direction of the platform.
>>>
>>> platform_orientation: Platform is a structure or vehicle that serves as
>>> a base for mounting sensors. Platforms include, but are not limited to,
>>> satellites, aeroplanes, ships, buoys, ground stations, and masts.
>>> Orientation is the clockwise angle with respect to North of the
>>> longitudinal (front-to-back) axis of the platform, which may be different
>>> than the platform course (see platform_course).
>>>
>>> platform_roll_rate: Platform is a structure or vehicle that serves as a
>>> base for mounting sensors. Platforms include, but are not limited to,
>>> satellites, aeroplanes, ships, buoys, ground stations, and masts. Roll rate
>>> is the rate of rotation about an axis (the X axis) that is perpendicular to
>>> the local vertical axis (the Z axis) and is coplanar with the nominal
>>> forward motion direction of the platform. Roll rate might not include
>>> changes in the ?at rest? rotation of the platform, which may change over
>>> time. The direction for positive values of roll rate is specified by an
>>> attribute named direction. The value of the direction attribute is
>>> "clockwise" if positive values of roll rate represent the right side of the
>>> platform rising as viewed by an observer on top of the platform facing
>>> forward. The value of the direction attribute is "anticlockwise" if
>>> positive values of roll rate represent the right side of the platform
>>> falling. The directionality of roll rate values is unspecified if no
>>> direction attribute is present.
>>>
>>> platform_pitch_rate: Platform is a structure or vehicle that serves as a
>>> base for mounting sensors. Platforms include, but are not limited to,
>>> satellites, aeroplanes, ships, buoys, ground stations, and masts. Pitch
>>> rate is the rate of rotation about an axis (the Y axis) that is
>>> perpendicular to both the local vertical axis (the Z axis) and the nominal
>>> forward motion direction of the platform. Pitch rate might not include
>>> changes in the ?at rest? rotation of the platform, which may change over
>>> time. The direction for positive values of pitch rate is specified by an
>>> attribute named direction. The value of the direction attribute is
>>> "clockwise" if positive values of pitch rate represent the front of the
>>> platform rising as viewed by an observer on top of the platform facing
>>> forward. The value of the direction attribute is "anticlockwise" if
>>> positive values of pitch rate represent the front of the platform falling.
>>> The directionality of pitch rate values is unspecified if no direction
>>> attribute is present.
>>>
>>> platform_yaw_rate: Platform is a structure or vehicle that serves as a
>>> base for mounting sensors. Platforms include, but are not limited to,
>>> satellites, aeroplanes, ships, buoys, ground stations, and masts. Yaw rate
>>> is the rate of rotation about the local vertical axis (the Z axis). Yaw
>>> rate might not include changes in the ?at rest? rotation of the platform,
>>> which may change over time. The direction for positive values of yaw rate
>>> is specified by an attribute named direction. The value of the direction
>>> attribute is "clockwise" if positive values of yaw rate represent the front
>>> of the platform moving to the right as viewed by an observer on top of the
>>> platform facing forward. The value of the direction attribute is
>>> "anticlockwise" if positive values of yaw rate represent the front of the
>>> platform moving to the left. The directionality of yaw rate values is
>>> unspecified if no direction attribute is present.
>>>
>>> platform_surge_rate: Platform is a structure or vehicle that serves as a
>>> base for mounting sensors. Platforms include, but are not limited to,
>>> satellites, aeroplanes, ships, buoys, ground stations, and masts. Surge
>>> rate is the rate of displacement along an axis (the X axis) that is
>>> perpendicular to the local vertical axis (the Z axis) and is coplanar with
>>> the nominal forward motion direction of the platform. Surge rate might not
>>> include changes in the ?at rest? position of the platform, which may change
>>> over time. The direction for positive values of surge rate is specified by
>>> an attribute named direction. The value of the direction attribute is
>>> "positive" if positive values of surge rate represent the platform moving
>>> forward as viewed by an observer on top of the platform facing forward. The
>>> value of the direction attribute is "negative" if positive values of surge
>>> rate represent the platform moving backward. The directionality of surge
>>> rate values is unspecified if no direction attribute is present.
>>>
>>> platform_sway_rate: Platform is a structure or vehicle that serves as a
>>> base for mounting sensors. Platforms include, but are not limited to,
>>> satellites, aeroplanes, ships, buoys, ground stations, and masts. Sway rate
>>> is the rate of displacement along an axis (the Y axis) that is
>>> perpendicular to both the local vertical axis (the Z axis) and the nominal
>>> forward motion direction of the platform. Sway rate might not include
>>> changes in the ?at rest? position of the platform, which may change over
>>> time. The direction for positive values of sway rate is specified by an
>>> attribute named direction. The value of the direction attribute is
>>> "positive" if positive values of sway rate represent the platform moving
>>> left as viewed by an observer on top of the platform facing forward. The
>>> value of the direction attribute is "negative" if positive values of sway
>>> rate represent the platform moving right. The directionality of sway rate
>>> values is unspecified if no direction attribute is present.
>>>
>>> platform_heave_rate: Platform is a structure or vehicle that serves as a
>>> base for mounting sensors. Platforms include, but are not limited to,
>>> satellites, aeroplanes, ships, buoys, ground stations, and masts. Heave
>>> rate is the rate of displacement along the local vertical axis (the Z
>>> axis). Heave rate might not include changes in the ?at rest? position of
>>> the platform, which may change over time. The direction for positive values
>>> of heave rate is specified by an attribute named direction. The value of
>>> the direction attribute is "positive" if positive values of heave rate
>>> represent the platform moving up as viewed by an observer on top of the
>>> platform facing forward. The value of the direction attribute is "negative"
>>> if positive values of heave rate represent the platform moving down. The
>>> directionality of heave rate values is unspecified if no direction
>>> attribute is present.
>>>
>>>
>>> Grace and peace,
>>>
>>>
>>> Jim
>>>
>>>
>>
>> _______________________________________________
>> CF-metadata mailing listCF-metadata at cgd.ucar.eduhttp://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>>
>>
>> --
>> John Helly, University of California, San Diego / San Diego Supercomputer Center / Scripps Institution of Oceanography / 760 840 8660 mobile / http://www.sdsc.edu/~hellyj
>> ORCID ID: orcid.org/0000-0002-3779-0603
>>
>>
>> --
>> [image: 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
>> 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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>> Twitter at _at_NOAANCEIclimate <https://twitter.com/NOAANCEIclimate> and
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>
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