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 <[email protected]> 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 <[email protected]> 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 > [email protected]http://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: [email protected] > o: +1 828 271 4900 > > *Connect with us on Facebook for climate > <https://www.facebook.com/NOAANCEIclimate> and ocean and geophysics > <https://www.facebook.com/NOAANCEIoceangeo> information, and follow us on > Twitter at @NOAANCEIclimate <https://twitter.com/NOAANCEIclimate> and > @NOAANCEIocngeo <https://twitter.com/NOAANCEIocngeo>. * > _______________________________________________ > CF-metadata mailing list > [email protected] > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata >
_______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
