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
>> <mailto: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
>>
>>
>>
>>
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>
> --
> 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
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