Hi John,
Your Q2 has been discussed at length. The local vertical axis is indeed local to the platform, as are the axes running front to back and left to right.
Your eagle eyes have indeed spotted something I missed in the yaw definition ' 'Yaw is a rotation about the axis of rotation' should I think read 'Yaw is a rotation about the local vertical axis'.
I HATE 'smart' quotes and Microsoft's mission to make every quote smart through auto-correction!
Cheers, Roy.
I have now retired but will continue to be active through an Emeritus Fellowship using this e-mail address.
________________________________
From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> on behalf of John Graybeal <jbgraybeal at mindspring.com>
Sent: 13 September 2018 16:38
To: CF Metadata List
Subject: Re: [CF-metadata] Platform Heave
It?s a brilliant effort, if I may say. I?ve been following and appreciating it (wanted it for a long time!) and I think it is very close.
If I may say so, it deserves a bit of time for everyone to catch up, before enshrinement. I have two questions I?d like to ask, and one editing nit.
Question 1: The last version I found is enclosed, but I can?t tell if it is the last version. (Please note the long tails of the emails make it extremely time-consuming to find the content when trying to catch up. Hence I have sent this without the long tail.)
This version does not seem to address Nan?s suggestion to put the platform description after the roll/pitch/etc description, which I also like. Still, I can see advantages both ways.
Question 2: The one concern I have, sorry if you dealt with it thoroughly, is about the expression in each definition that reads something like "Roll is a rotation about an axis that is perpendicular to the local vertical axis and is coplanar with the nominal forward motion direction of the platform.? I may be mis-remembering, but from my airplane navigation days my understanding is that the role is around the axis that points out the front of the airplane. If the airplane is pitched up, the roll is around the pitched-up vector; if the airplane is yawing to the right, the roll is around the actual direction, not the travel direction. This is important at small scales when dealing with the spherical coordinate math necessary to point telescopes; it?s important at large scales if you imagine a fighter jet flying vertically up or down, and executing a roll (the roll axis is definitely not perpendicular to the local vertical axis in this case, unless you mean ?platform local?, which I believe is how it is defi
ned and I?m pretty sure is how it is measured by the accelerometers). I believe that satellites work the same way also?once they define ?front?, the measurements and calculations for roll are all around where front is, and similar patterns apply for pitch (measured relative to a line perpendicular to front-back axis directly through the wings) and yaw (measured around an axis vertical to the airplane local?note that the definitions for yaw include "Yaw is a rotation about the axis of rotation?, and appear to have lost the description of what the axis of rotation *is*.
I cite Wikipedia as my authority, not just because it matches my memory but also because it is footnoted, and refers to both airplanes and satellites using this reference frame.
Finally, my editing nit is that these definitions have replaced smart apostrophes with question marks, I assume dumb apostrophes are the order of the day.
John
platform_roll_starboard_down: 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 that is perpendicular to the local vertical 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 axis of rotation. The ?at rest? rotation of the platform may change over time. "Starboard down" indicates that positive values of roll represent the right side of the platform falling as viewed by an observer on top of the platform facing forward.
platform_roll_starboard_up: 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 that is perpendicular to the local vertical 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 axis of rotation. The ?at rest? rotation of the platform may change over time. "Starboard up" indicates that positive values of roll represent the right side of the platform rising as viewed by an observer on top of the platform facing forward.
platform_roll_rate_starboard_down: 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 that is perpendicular to the local vertical axis and is coplanar with the nominal forward motion direction of the platform. Roll rate might not include changes to the ?at rest? rotation of the platform with respect to the axis of rotation, which may change over time. "Starboard down" indicates that positive values of roll rate represent the right side of the platform falling as viewed by an observer on top of the platform facing forward.
platform_roll_rate_starboard_up: 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 that is perpendicular to the local vertical axis and is coplanar with the nominal forward motion direction of the platform. Roll rate might not include changes to the ?at rest? rotation of the platform with respect to the axis of rotation, which may change over time. "Starboard up" indicates that 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.
platform_pitch_fore_up: 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 that is perpendicular to both the local vertical 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 axis of rotation. The ?at rest? rotation of the platform may change over time. "Fore up" indicates that positive values of pitch represent the front of the platform rising as viewed by an observer on top of the platform facing forward.
platform_pitch_fore_down: 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 that is perpendicular to both the local vertical 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 axis of rotation. The ?at rest? rotation of the platform may change over time. "Fore down" indicates that positive values of pitch represent the front of the platform falling as viewed by an observer on top of the platform facing forward.
platform_pitch_rate_fore_up: 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 that is perpendicular to both the local vertical axis and the nominal forward motion direction of the platform. Pitch rate might not include changes to the ?at rest? rotation of the platform with respect to the axis of rotation, which may change over time. "Fore up" indicates that positive values of pitch rate represent the front of the platform rising as viewed by an observer on top of the platform facing forward.
platform_pitch_rate_fore_down: 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 that is perpendicular to both the local vertical axis and the nominal forward motion direction of the platform. Pitch rate might not include changes to the ?at rest? rotation of the platform with respect to the axis of rotation, which may change over time. "Fore down" indicates that positive values of pitch rate represent the front of the platform falling as viewed by an observer on top of the platform facing forward.
platform_yaw_fore_starboard: 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 axis of rotation. Yaw is relative to the ?at rest? rotation of the platform with respect to the axis of rotation. The ?at rest? rotation of the platform may change over time. "Fore starboard" indicates that 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.
platform_yaw_fore_port: 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 axis of rotation. Yaw is relative to the ?at rest? rotation of the platform with respect to the axis of rotation. The ?at rest? rotation of the platform may change over time. "Fore port" indicates that positive values of yaw represent the front of the platform moving to the left as viewed by an observer on top of the platform facing forward.
platform_yaw_rate_fore_starboard: 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 axis of rotation. Yaw rate might not include changes to the ?at rest? rotation of the platform with respect to the axis of rotation, which may change over time. "Fore starboard" indicates that 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.
platform_yaw_rate_fore_port: 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 axis of rotation. Yaw rate might not include changes to the ?at rest? rotation of the platform with respect to the axis of rotation, which may change over time. "Fore port" indicates that positive values of yaw rate represent the front of the platform moving to the left as viewed by an observer on top of the platform facing forward.
platform_surge_fore: 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 that is perpendicular to the local vertical 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 axis of displacement. The ?at rest? position of the platform may change over time. "Fore" indicates that positive values of surge represent the platform moving forward as viewed by an observer on top of the platform facing forward.
platform_surge_aft: 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 that is perpendicular to the local vertical 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 axis of displacement. The ?at rest? position of the platform may change over time. "Aft" indicates that positive values of surge represent the platform moving backward as viewed by an observer on top of the platform facing forward.
platform_surge_rate_fore: 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 that is perpendicular to the local vertical axis and is coplanar with the nominal forward motion direction of the platform. Surge rate might not include changes to the ?at rest? position of the platform with respect to the axis of displacement, which may change over time. "Fore" indicates that positive values of surge rate represent the platform moving forward as viewed by an observer on top of the platform facing forward.
platform_surge_rate_aft: 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 that is perpendicular to the local vertical axis and is coplanar with the nominal forward motion direction of the platform. Surge rate might not include changes to the ?at rest? position of the platform with respect to the axis of displacement, which may change over time. "Aft" indicates that positive values of surge rate represent the platform moving backward as viewed by an observer on top of the platform facing forward.
platform_sway_port: 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 that is perpendicular to both the local vertical 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 axis of displacement. The ?at rest? position of the platform may change over time. "Port" indicates that positive values of sway represent the platform moving left as viewed by an observer on top of the platform facing forward.
platform_sway_starboard: 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 that is perpendicular to both the local vertical 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 axis of displacement. The ?at rest? position of the platform may change over time. "Starboard" indicates that positive values of sway represent the platform moving right as viewed by an observer on top of the platform facing forward.
platform_sway_rate_port: 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 that is perpendicular to both the local vertical axis and the nominal forward motion direction of the platform. Sway rate may not include changes to the ?at rest? position of the platform with respect to the axis of displacement, which may change over time. "Port" indicates that positive values of sway rate represent the platform moving left as viewed by an observer on top of the platform facing forward.
platform_sway_rate_starboard: 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 a displacement along an axis that is perpendicular to both the local vertical axis and the nominal forward motion direction of the platform. Sway rate may not include changes to the ?at rest? position of the platform with respect to the axis of displacement, which may change over time. "Starboard" indicates that positive values of sway rate represent the platform moving right as viewed by an observer on top of the platform facing forward.
platform_heave_up: 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. Heave is relative to the ?at rest? position of the platform with respect to the axis of displacement. The ?at rest? position of the platform may change over time. "Up" indicates that positive values of heave represent the platform moving up as viewed by an observer on top of the platform facing forward.
platform_heave_down: 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. Heave is relative to the ?at rest? position of the platform with respect to the axis of displacement. The ?at rest? position of the platform may change over time. "Down" indicates that positive values of heave represent the platform moving down as viewed by an observer on top of the platform facing forward.
platform_heave_rate_up: 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. Heave rate may not include changes to the ?at rest? position of the platform with respect to the axis of displacement, which may change over time. "Up" indicates that positive values of heave rate represent the platform moving up as viewed by an observer on top of the platform facing forward.
platform_heave_rate_down: 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. Heave rate may not include changes to the ?at rest? position of the platform with respect to the axis of displacement, which may change over time. "Down" indicates that positive values of heave rate represent the platform moving down as viewed by an observer on top of the platform facing forward.
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).
---------------------------------------
John Graybeal
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650-450-1853
skype: graybealski
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