Dear Jim et al.,
Thank you again for all the work on these names and their definitions. I have
now caught up with all the comments in the discussion and I think the names as
written most recently by Jim in
http://mailman.cgd.ucar.edu/pipermail/cf-metadata/2018/020513.html are looking
very good. All the recent comments seem to indicate unanimous support (with a
couple of minor corrections to the yaw definition text).
The definitions are great and using pairs of names is a neat solution to all
the questions regarding reference frames and sign conventions. There has been
some discussion of the order of the sentences in the definition, i.e. whether
the quantity can be described first, followed by the general description of
'platform'. Jim pointed out that in many standard name definitions the
sentences are ordered in the same way as the components of the name itself.
Often I have constructed them that way because it gives some logical structure
to the text, rather than just adding the sentences in some random order.
However, there is no hard and fast rule and sometimes we do adjust the order of
the sentences so that the text flows more naturally. For example, we recently
added a lot of new names for sea surface wave spectra, such as
sea_surface_primary_swell_wave_directional_spread, in which the first sentence
of each definition summarizes the meaning of the quantity as a whole before
going into further detail about the individual terms. I don't see any problem
about reordering the platform definitions in the way Nan has suggested, e.g.
platform_yaw_fore_starboard: Yaw is a rotation about the local vertical axis. 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 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.
Unless anyone objects, I will write the definitions this way round when I add
them to the standard name table.
There is another (technical) point that I need to raise before formally
accepting these names. Some of the names are new, e.g. the surge and sway
quantities, so there is no problem about adding pairs of these names straight
into the table as new entries. During the discussion it was mentioned that
'heave' would also be new. In fact, I added names platform_heave and
platform_heave_rate to the standard name table in V58 on 7th August with
definitions that I thought we had agreed at that point. (This was just before I
went on leave and it didn't get announced on the list, so I'll post details of
that update separately.) For the heave names and the existing yaw/pitch/roll
names we now want to introduce pairs of names to allow for the possible use of
opposing sign conventions and this raises a question about how to construct the
aliases.
We had a similar case some years ago in which it was realised that the existing
name surface_carbon_dioxide_mole_flux gave no indication of its sign
convention. There was some discussion over whether existing data sets might
treat the upward flux as positive and downwards as negative, or vice versa.
There was no real way of answering this question, so to avoid invalidating any
existing data, I added two new names
surface_downward_mole_flux_of_carbon_dioxide and
surface_downward_mole_flux_of_carbon_dioxide and listed
surface_carbon_dioxide_mole_flux as the alias of both. The definitions of the
new terms both contain the sentences 'The standard name
surface_carbon_dioxide_mole_flux is deprecated because it does not specify in
which direction the flux is positive. Any data having the standard name
surface_carbon_dioxide_mole_flux should be examined carefully to determine
which sign convention was used.' This seemed like a pragmatic approach to
solving the problem of adding a pair of new names while not making any
assumptions about the sign conventions already in use. I would argue that a
similar approach would also make sense for the heave/yaw/pitch/roll names,
e.g., platform_yaw_fore_starboard and platform_yaw_fore_port would both have an
alias of platform_yaw_angle and an explanatory sentence in the definitions
similar to that in the carbon_dioxide name.
There is just one problem with adopting my suggested approach - it requires a
change to the conventions. CF trac #155/GitHub issue #132 discusses the fact
the current XML schema for the standard name table actually doesn't allow for
two names to have the same alias. Personally, I think there are good reasons
why this should be allowed, so as to cope with cases like the ones currently
under discussion, and therefore we should change the schema. Do others agree
with this approach, or does anyone have a better idea?
Best wishes,
Alison
------
Alison Pamment Tel: +44 1235 778065
NCAS/Centre for Environmental Data Archival Email: alison.pamm...@stfc.ac.uk
STFC Rutherford Appleton Laboratory
R25, 2.22
Harwell Oxford, Didcot, OX11 0QX, U.K.
From: CF-metadata <cf-metadata-boun...@cgd.ucar.edu> On Behalf Of Lowry, Roy K.
Sent: 13 September 2018 20:11
To: Jim Biard <jbi...@cicsnc.org>; cf-metadata@cgd.ucar.edu
Subject: Re: [CF-metadata] Platform Heave
Hi Jim,
Interesting article that answers some of my questions about what we've been
defining here in terms of platform-local axes and 'real world' co-ordinate
reference systems.
Cheers, Roy.
I have now retired but will continue to be active through an Emeritus
Fellowship using this e-mail address.
________________________________________
From: CF-metadata on behalf of Jim Biard
Sent: 13 September 2018 19:39
To: mailto:cf-metadata@cgd.ucar.edu
Subject: Re: [CF-metadata] Platform Heave
I only just located this wikipedia article. It describes the different axes
conventions that are in common use and the differences between them.
https://en.wikipedia.org/wiki/Axes_conventions
https://en.wikipedia.org/wiki/Axes_conventions
en.wikipedia.org
In ballistics and flight dynamics, axes conventions are standardized ways of
establishing the location and orientation of coordinate axes for use as a frame
of reference.Mobile objects are normally tracked from an external frame
considered fixed. Other frames can be defined on those mobile objects to deal
with relative positions for other objects.
On 9/13/18 12:15 PM, Lowry, Roy K. wrote:
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 on behalf of John Graybeal
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 defined 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).
---------------------------------------
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mailto:jbgrayb...@mindspring.com
650-450-1853
skype: graybealski
linkedin: http://www.linkedin.com/in/johngraybeal/
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