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
>>
>>
>
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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
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