Dear Roy and Jim,
Thanks again both for your help.
Both your replies are saying that referring to direction of motion
for measuring yaw is a bad idea, and in any case it doesn't apply to
stationary platforms (which presumably have some means of determining
their own orientation relative to concepts such as 'up', 'north',
etc.) You are both advising against saying 'mean orientation' and I
agree that it's not really a well-defined concept.
I like Roy's suggested text which refers to the platform's own axis
to define yaw. So the full definition of platform_yaw_angle would be:
'Standard names for "platform" describe the motion and orientation of
the vehicle from which observations are made. Platforms include, but
are not limited to, satellites, aeroplanes, ships, instruments and
buoys. "Yaw" means rotation of the platform in the horizontal plane
about its vertical/Z axis. The vertical/Z axis, also known as the
"yaw axis", is an imaginary line running vertically through the
platform and through its center of gravity. In yaw motion, the
platform rotates clockwise or counter clockwise in the horizontal,
relative to its orientation, which has the standard name
platform_orientation. Platform yaw angle is the angle at a given
instant between the platform's longitudinal/X axis and the position
of that axis with high frequency variations (e.g. the effect of
surface waves on a ship) removed. Zero yaw angle means the
longitudinal axis is aligned with the platform_orientation. The usual
sign convention is that yaw angle is measured positive when the front or
leading
edge of the platform is rotated clockwise from the
platform_orientation.'
Okay?
Like Roy, I had wondered whether 'platform_orientation' should really
be an instantaneous quantity or something with high frequency
variability removed. If it is the latter (which I think was probably
the original intention of the standard name) then we should amend the
definition as follows:
'Standard names for "platform" describe the motion and orientation of
the vehicle from which observations are made. Platforms include, but
are not limited to, satellites, aeroplanes, ships, instruments and
buoys. The platform orientation is the direction in which the "front"
or longitudinal axis of the platform is pointing with high frequency
variations (e.g. the effect of surface waves on a ship) removed.
(This is not necessarily the same as the direction in which the
platform is travelling, called platform_course).'
Okay?
As an additional point, I note that besides the names already
discussed in this thread, there are a further 11 existing platform
names. I will include the new text for 'platform' in their
definitions as part of the August standard names update.
Best wishes,
Alison
________________________________
From: Lowry, Roy K. <[email protected]>
Sent: 25 July 2018 16:35:27
To: Pamment, Alison (STFC,RAL,RALSP); [email protected]
Subject: Re: [CF-metadata] Platform Heave
Hi again,
This is an area where it is easy to get tied up in knots because
there are multiple reference frames. If we talk ships then there is
the platform_orientation (or heading) which is measured using a
gyro-compass - a stabilised instrument that eliminates high-frequency
variations in where the bow is actually pointing and provides the
zero reference point for yaw.
The concept of 'travel' relates to another reference frame external
to the platform - say a GPS CRS - but yaw only has relevance to the
platform's internal reference frame. So you are right that bringing
'direction of travel' into a definition of yaw is a bad thing even
though it's reasonably common practice to do so.
Mean orientation is also possibly best avoided as the
platform_orientation isn't necessarily determined by averaging
instantaneous longitudinal axis orientations. It could be - and
often is - measured by something that has greater inertia than the
platform.
So how about using :
Platform yaw angle is the angle at a given instant between the
platform's longitudinal/X axis and the position of that axis with
high frequency variations (e.g. the effect of surface waves on a
ship) removed. Zero yaw angle means the longitudinal axis is aligned
with the platform_orientation. The usual sign convention is that yaw
angle is measured positive when the front or leading edge of the
platform is rotated clockwise from the platform_orientation.
This raises the question as to whether the platform_orientation
definition should have the clarification 'with high-frequency
variability removed' added. This would be an explicit statement of
what - to me at least - is commonly understood meaning of 'heading'.
Does that help?
Cheers, Roy.
I have now retired but will continue to be active through an Emeritus
Fellowship using this e-mail address.
________________________________
From: CF-metadata <[email protected]> on behalf of
Alison Pamment - UKRI STFC <[email protected]>
Sent: 25 July 2018 14:37
To: [email protected]
Subject: Re: [CF-metadata] Platform Heave
Hi Roy and Jim,
Thanks for your quick comments on the definitions. I have just been
looking again at the suggested text for yaw_angle:
'Platform yaw angle is the angle between the platform's
longitudinal/X axis and the direction of travel. Zero yaw angle means
the longitudinal axis is aligned with the direction of travel, or a
reference direction if the platform is stationary. The usual sign
convention is that yaw angle is measured positive when the front or
leading edge of the platform is rotated clockwise from its
orientation (which has the standard name platform_orientation).'
The problem is how to describe the reference direction which the
angle is calculated relative to. I started out by talking about
'direction of travel' and later referred to 'platform_orientation'.
The definition of platform_orientation says 'The platform orientation
is the direction in which the "front" or longitudinal axis of the
platform is pointing (not necessarily the same as the direction in
which it is travelling, called platform_course).' I've realised my
new definition doesn't really make sense if direction of travel and
orientation aren't the same (and clearly they can be different).
Also, if 'orientation' is the instantaneous direction of the
longitudinal axis, then presumably it includes yaw angle, so it isn't
the right reference for measuring yaw.
I've revised the text as follows:
'Platform yaw angle is the angle between the platform's
longitudinal/X axis and the platform's mean orientation (i.e. its
orientation not including high frequency variations due to swaying
and rocking motions, for example, ship motions caused by the passing
of sea surface waves). Zero yaw angle means the longitudinal axis is
aligned with the mean orientation. The usual sign convention is that
yaw angle is measured positive when the front or leading edge of the
platform is rotated clockwise from its mean orientation (which has
the standard name platform_orientation).
Does it sound okay to refer to a 'mean orientation' in this way? I'm
having trouble thinking of a better wording!
Best wishes,
Alison
------
Alison Pamment Tel: +44 1235 778065
NCAS/Centre for Environmental Data Archival Email:
[email protected]
STFC Rutherford Appleton Laboratory
R25, 2.22
Harwell Oxford, Didcot, OX11 0QX, U.K.
-----Original Message-----
From: CF-metadata <[email protected]> On Behalf Of
Alison Pamment - UKRI STFC
Sent: 25 July 2018 13:12
To: Hamilton, Steve <[email protected]>; [email protected]
Subject: Re: [CF-metadata] Platform Heave
Dear Steve, Nan, et al,
Thank you for proposing new standard names for platform_heave and
improved definitions for existing names for platform pitch, roll and
yaw. Thank you also to all those who submitted comments about these
names.
Regarding Steve's proposals for new names, the discussion seems to
have reached consensus on the quantities themselves.
Until now, our usual explanatory sentence for 'platform' has said
'Standard names for platform describe the motion and orientation of
the vehicle from which observations are made e.g. aeroplane, ship or
satellite.' Nan has suggested extending the list of possible
platforms, which seems fair enough, so we would now have 'Standard
names for platform describe the motion and orientation of the vehicle
from which observations are made. Platforms include, but are not
limited to, satellites, aeroplanes, ships, instruments, and buoys.'
I've added this into the definitions of Steve's names, leading to:
platform_heave (m)
'Standard names for "platform" describe the motion and orientation of
the vehicle from which observations are made. Platforms include, but
are not limited to, satellites, aeroplanes, ships, instruments, and
buoys. "Heave" means the vertical displacement of a platform
(positive upwards) over a measurement time interval.'
platform_heave_rate (m s-1)
'Standard names for "platform" describe the motion and orientation of
the vehicle from which observations are made. Platforms include, but
are not limited to, satellites, aeroplanes, ships, instruments, and
buoys "Heave" means the vertical displacement of a platform (positive
upwards) over a measurement time interval. "Heave rate" means the
rate of change of vertical displacement of the platform over a
measurement time interval.'
These two names are accepted for publication in the standard name
table and will be added in the next update, planned for 6th August.
We have six existing platform pitch, roll and yaw names:
platform_pitch_angle (degree)
platform_pitch_rate (degree s-1)
platform_roll_angle (degree)
platform_roll_rate (degree s-1)
platform_yaw_angle (degree)
platform_yaw_rate (degree s-1)
Nan has suggested the following definitions, based on
https://en.wikipedia.org/wiki/Ship_motions. (A quick search of other
online sources yields definitions consistent with these).
Ship motions - Wikipedia<https://en.wikipedia.org/wiki/Ship_motions>
en.wikipedia.org
Ship motions are defined by the six degrees of freedom that a ship,
boat or any other craft can experience.
Pitch
The up/down rotation of a platform about its transverse/Y axis. The
transverse/Y axis, lateral or pitch axis is an imaginary line running
horizontally across the platform and through its center of gravity. A
pitch motion is an up-or-down movement of the bow and stern of the
platform.
Roll
The tilting rotation of a platform about its longitudinal/X axis. The
longitudinal/X axis, or roll axis, is an imaginary line running
horizontally through the length of the platform, through its center
of gravity, and parallel to the waterline. A roll motion is a
side-to-side or port-starboard tilting motion of the superstructure
around this axis.
Yaw
The turning rotation of a platform about its vertical/Z axis. The
vertical/Z axis, or yaw axis, is an imaginary line running vertically
through the platform and through its center of gravity. A yaw motion
is a side-to side movement of the bow and stern of the ship.
These are useful and concise definitions. I suggest that we don't
refer anywhere to 'ship', 'bow' or 'stern', since we want the
definitions to apply to all possible platforms. I'm thinking also
that 'port' and 'starboard' may apply to ships and aeroplanes, but
perhaps not to a satellite, so are probably best avoided. Similarly,
'waterline' only applies to maritime platforms. I suggest the
following amendments to make the definitions as generic as possible:
Pitch
"Pitch" means rotation of the platform in the vertical plane about
its transverse/Y axis. The transverse/Y axis, also known as the
"lateral axis" or "pitch axis", is an imaginary line running
horizontally across the platform and through its center of gravity.
In pitch motion, the leading edge of the platform moves vertically
upwards while the rear moves vertically downwards, and vice versa.
Roll
"Roll" means rotation of the platform in the vertical plane about its
longitudinal/X axis. The longitudinal/X axis, also known as the "roll
axis", is an imaginary line running horizontally through the length
of the platform and through its center of gravity. In roll motion,
the platform tilts such that one side moves vertically upwards while
the other moves vertically downwards, and vice versa.
Yaw
"Yaw" means rotation of the platform in the horizontal plane about
its vertical/Z axis. The vertical/Z axis, also known as the "yaw
axis", is an imaginary line running vertically through the platform
and through its center of gravity. In yaw motion, the platform
rotates clockwise or counter clockwise in the horizontal, relative to
its orientation, which has the standard name platform_orientation.
Are these okay?
For names such as platform_view_angle and platform_zenith_angle we
also describe how the angle itself is measured. We should do the same
for pitch, roll and yaw angles while we are in the process of
updating the definitions. I have come up with the following:
Pitch angle
Platform pitch angle is the angle between the local horizontal and
the platform's longitudinal/X axis. Zero pitch angle means the
longitudinal axis is horizontal. The usual sign convention is that
pitch angle is measured positive when the front or leading edge of
the platform is elevated above the horizontal, negative when it is
below the horizontal.
Roll angle
Platform roll angle is the angle between the local horizontal and the
platform's lateral/Y axis. Zero roll angle means the lateral axis is
horizontal. The usual sign convention is that roll angle is measured
positive when the right hand edge of the platform (when viewing
towards the orientation direction or "front" of the platform) is
elevated above the horizontal, negative when it is below the horizontal.
Yaw angle
Platform yaw angle is the angle between the platform's longitudinal/X
axis and the direction of travel. Zero yaw angle means the
longitudinal axis is aligned with the direction of travel, or a
reference direction if the platform is stationary. The usual sign
convention is that yaw angle is measured positive when the front or
leading edge of the platform is rotated clockwise from its
orientation (which has the standard name platform_orientation).
Just so we can see a couple of examples of pulling all this together,
I've written out the full revised definitions of platform
platform_pitch_angle and platform_pitch_rate below.
platform_pitch_angle (degree)
'Standard names for "platform" describe the motion and orientation of
the vehicle from which observations are made. Platforms include, but
are not limited to, satellites, aeroplanes, ships, instruments and
buoys. "Pitch" means rotation of the platform in the vertical plane
about its transverse/Y axis. The transverse/Y axis, also known as the
"lateral axis" or "pitch axis", is an imaginary line running
horizontally across the platform and through its center of gravity.
In pitch motion, the leading edge of the platform moves vertically
upwards while the rear moves vertically downwards, and vice versa.
Platform pitch angle is the angle between the local horizontal and
the platform's longitudinal/X axis. Zero pitch angle means the
longitudinal axis is horizontal. The usual sign convention is that
pitch angle is measured positive when the front or leading edge of
the platform is elevated above the horizontal, negative when it is
below the horizontal.'
platform_pitch_rate (degree s-1)
'Standard names for "platform" describe the motion and orientation of
the vehicle from which observations are made. Platforms include, but
are not limited to, satellites, aeroplanes, ships, instruments and
buoys. "Pitch" means rotation of the platform in the vertical plane
about its transverse/Y axis. The transverse/Y axis, also known as the
"lateral axis" or "pitch axis", is an imaginary line running
horizontally across the platform and through its center of gravity.
In pitch motion, the leading edge of the platform moves vertically
upwards while the rear moves vertically downwards, and vice versa.
The quantity with standard name platform_pitch_rate is the change per
unit time in the quantity with standard name platform_pitch_angle.'
The roll and yaw definitions would be constructed similarly.
The pitch/roll/yaw names are still under discussion. I'd welcome
further comments on these.
Best wishes,
Alison
------
Alison Pamment Tel: +44 1235 778065
NCAS/Centre for Environmental Data Archival Email:
[email protected]
STFC Rutherford Appleton Laboratory
R25, 2.22
Harwell Oxford, Didcot, OX11 0QX, U.K.
-----Original Message-----
From: CF-metadata <[email protected]> On Behalf Of
Hamilton, Steve
Sent: 11 July 2018 10:52
To: [email protected]
Subject: Re: [CF-metadata] Platform Heave
Hi Nan,
I agree expanding on the existing standard name descriptions does
make sense and standardising for _rate and _angle
What you suggest below seems acceptable
Thanks
Steve
-----Original Message-----
From: CF-metadata <[email protected]> On Behalf Of Nan
Galbraith
Sent: 10 July 2018 17:39
To: [email protected]
Subject: Re: [CF-metadata] Platform Heave
Hi Alison, Steve, and all -
Since we have a little time to finalize this, could we also consider
updating the definitions of platform_pitch_angle, platform_roll_angle
and platform_yaw_angle?
Currently, these all say 'Standard names for platform describe the
motion and orientation of the vehicle from which observations are
made e.g. aeroplane, ship or satellite.'
John Helly pointed to the helpful Wikipedia page for ship motion,
https://en.wikipedia.org/wiki/Ship_motions. The suggestions below are
merged from different sections of that page, and might be a little
... long, but I'd also like to append something like 'Platforms
include but are not limited to satellites, aeroplanes, ships,
instruments, and buoys.'
Pitch
The up/down rotation of a platform about its transverse/Y axis. The
transverse/Y axis, lateral or pitch axis is an imaginary line running
horizontally across the platform and through its center of gravity. A
pitch motion is an up-or-down movement of the bow and stern of the
platform.
Roll
The tilting rotation of a platform about its longitudinal/X axis. The
longitudinal/X axis, or roll axis, is an imaginary line running
horizontally through the length of the platform, through its center
of gravity, and parallel to the waterline. A roll motion is a
side-to-side or port-starboard tilting motion of the superstructure
around this axis.
Yaw
The turning rotation of a platform about its vertical/Z axis. The
vertical/Z axis, or yaw axis, is an imaginary line running vertically
through the platform and through its center of gravity.
A yaw motion is a side-to side movement of the bow and stern of the
ship.
And we had something like this for heave:
platform_heave (m) = upwards vertical displacement
I suppose these could also be applied to platform_*_rates.
Regards -
Nan
On 7/4/18 4:47 AM, Alison Pamment - UKRI STFC wrote:
Dear Steve, > > Thank you for your message and apologies for not
having processed
> your proposals as yet. I have been working on the CMIP names, but
> they are reaching a conclusion and I will shortly be looking
through > the many other proposals that have been waiting for
attention. > > A quick look through the discussion of your names
shows they are > pretty much agreed. You need take no further action
at this time - I > will check that the names and definitions are
clear and consistent > with existing names and get back to you on the
list with any final > comments or questions. Version 56 of the
standard name table will be > published later today - I think we can
probably finalise your names > in time for version 57. > > Best
wishes, Alison
________________________________
From: Hamilton, Steve <[email protected]>
Sent: 03 July 2018 09:12
Please can you advise if this standard name has now been accepted and
when it will be included in the CF Standard Names
If there is something else to do please let me know
Thanks
Steve
________________________________
From: Jim Biard <[email protected]<mailto:[email protected]>>
Sent: 01 June 2018 22:56
Nan,
Thanks for pulling things back in. I very much like the idea of
keeping technology or specific methods out of the definition if at
all possible, so I like your proposal. I expect we should include
platform in the definition, as well as an indication that this is
dynamic (over time). How about these definitions?
platform_heave (m) = upwards vertical displacement of a platform over
a measurement time interval platform_heave_rate (m s-1) = upwards rate
of change in vertical displacement of a platform over a measurement
time interval They leave out some detail but capture the relative
nature of the quantities.
(In my mind, the primary detail being left out is the 'net zero'
nature of the quantities, which gets back to defining the
'moving-mean' sea level reference point.) Grace and peace,
Jim
On 6/1/18 11:23 AM, Nan Galbraith wrote:
Hi all -
The latest version is confusing to me. The term 'a platform that is
nominally at rest' does not apply to many platforms for which heave is
calculated; the original version of that, 'a moving object above the
vertical level of that object when stationary' was maybe a little
more clear... if also a little wordy.
And, the term 'vertical displacement determined by integrating
vertical accelerations' may also not apply - I've been looking at the
different ways heave is calculated, and there are a few: 'Heave can be
computed from GPS RTK height measurements and from vertical
accelerations measured by linear accelerometers'
Why not keep it simple: platform_heave (m) = upwards vertical
displacement? Do we need to be more specific than that?
Thanks - Nan
From: Lowry, Roy K.
Sent: 30 May 2018 21:37
An afterthought. Heave is conventionally positive upwards so to make
this clear I would add the word 'upwards' thus:
platform_heave (m) = upwards vertical displacement determined by
integrating vertical accelerations of a platform that is nominally
at rest.
platform_heave_rate (m s-1) = upwards vertical velocity determined
by integrating vertical accelerations of a platform that is
nominally at rest.
Cheers. Roy.
----------------------------------------------------------------------
--
From: Lowry, Roy K. <[email protected]<mailto:[email protected]>
Sent: 30 May 2018 21:02
Thanks Jim,
That work for me.
Cheers, Roy.
----------------------------------------------------------------------
--
From: Jim Biard <[email protected]>
Sent: 30 May 2018 18:39
Roy,
So, heave is integrated vertical acceleration? How about
platform_heave (m) = vertical displacement determined by integrating
vertical accelerations of a platform that is nominally at rest.
platform_heave_rate (m s-1) = vertical velocity determined by
integrating vertical accelerations of a platform that is nominally
at rest.
Jim
On 5/27/18 5:38 AM, Lowry, Roy K. wrote:
Hi Jim,
Does
"Heave" is a term used to describe the vertical displacement
of a moving object above the vertical level of that object
when stationary.
help by getting rid of the semantically-loaded word 'height'?
If not, what would?
I think the confusion is because you are thinking of heave in
terms of position within a reference frame. To think of it as the
vertical displacement between a real platform and a massless
platform is misleading- such considerations are part of the
derivation of wave height from high frequency heave measurements,
which isn't relevant to a discussion of the raw measurement. It's
also worth bearing in mind that whilst the debate has focused on
platforms floating on the sea surface, the concept of heave could
in theory be applied to objects in the atmosphere.
In practice, heave is measured by accelerometers that are usually
combined with tilt sensors that give pitch, roll and yaw. Hence,
it is totally decoupled from any reference outside the platform.
To answer your last muse, to get heave from a high frequency
height relative to datum time series the method would need to
determine the height of the object when 'stationary'. In the case
of objects on the sea, 'stationary' is considered to be a flat
calm sea (i.e. no waves), which can be approximated by averaging
the raw time series. So, heave could be approximated by
differencing the raw and averaged data. However, I can't think
why
anybody would want to do that.
Cheers, Roy.
----------------------------------------------------------------------
--
From:Jim Biard <[email protected]><mailto:[email protected]>
Sent: 26 May 2018 23:18
My biggest concern is that the standard name definition makes it
clear in some fashion or other that this is a measure of
deviations from some lower frequency (or low-pass filtered)
measure of vertical position. (As are sway and surge in relation
to their corresponding horizontal coordinates.) As was pointed
out, heave is used in certain communities, so it's reasonable to
provide a standard name, but it seems rather imprecise as it has
been described so far.
If I have understood the explanations correctly, a time series of
platform height relative to a fixed datum that has sufficient
precision and frequency would fully represent the heave along
with
the more slowly varying effects of tide, waves, etc. So is heave,
as usually used, the first-order instantaneous difference between
the height of an actual platform and the height of a massless
ideal platform that would maintain a fixed offset relative to the
sea surface? And, just out of curiosity, how would a time series
of instantaneous measures of height relative to a fixed datum be
separated in practice into heave and "non-heave" height?
Getting back on track, it seems to me that the definition
ought to
somehow assist the reader in understanding how heave relates to
other measures of height.
On Sat, May 26, 2018 at 3:11 AM, Lowry, Roy K. wrote:
Dear Jim and John,
Heave is indeed a height relative to a datum, that datum
being
the calm sea surface, which is a local short interval mean
sea
level that isn't linked into any global reference system.
Indeed the 'datum' moves relative to the rest of the world -
but not the platform - as tide rises and falls so many would
prefer to call it an 'instrument zero' rather than a 'datum'.
Heave is therefore a very different measurement to any sea
level parameter and is the raw measurement recorded at high
(Hz to kHz) frequency as a time series by floating wave
instruments such as waveriders and shipborne wave recorders.
It therefore cannot be sensibly described by the same or
similar Standard Name as a measurement of height above a
globally referenced datum like long-term mean sea level or
geoid. Whilst the Standard Name could be
'platform_height_above_calm_sea_surface' or
'platform_height_above_stationary_position' I would argue
that
'heave' is a term from the same domain vocabulary as 'pitch',
'roll' and 'yaw' and therefore should be used.
John is right to point out that the heave measurement is
affected by the nature of the platform with a 250,000 tonne
supertanker moving up and down much less than a rowing
boat in
a given wave climate, especially a wind sea. That was what
was
behind the SBWR corrections based on platform dimensions set
up by Laurie Draper and Tom Tucker back in the 1980s.
Cheers, Roy.
----------------------------------------------------------------------
--
From: John Helly <[email protected]>
Sent: 26 May 2018 04:48
Can't let go of this yet.
If you think about the inverse problem of deriving the sea
surface elevation from the heave you would have to account
for
the latency of ship motion relative to the sea-surface. A
wave passing under a ship induces motions that are not
instantaneous either in attack or decay.
J.
On 5/25/18 20:42, John Helly wrote:
I believe it's a synonym within the oceanographic
community for the vertical motion of an ocean-going
platform.
https://en.wikipedia.org/wiki/Ship_motions
Ship motions - Wikipedia
<https://en.wikipedia.org/wiki/Ship_motions><https://en.wikipedia.org/
wiki/Ship_motions>
en.wikipedia.org
<http://en.wikipedia.org><http://en.wikipedia.org>
Ship motions are defined by the six degrees of freedom
that a ship, boat or any other craft can experience.
Could just be jargon but it strike me as more complex:
nonetheless a vertical position relative to a datum, but
the buoyancy, stability and momentum of the platform are
implied as part of the dynamics. It seems that the datum
is not a geophysical one alone but confounded with the
'normal' waterline for a platform so it may be
relative to
the water level in which the platform is embedded. That's
a tough one. Two different platforms on the same sea
surface would have different 'heave', for example.
J.
On 5/25/18 19:54, Jim Biard wrote:
Hi.
I get and endorse the need for pitch, roll, and yaw,
but I remain perplexed about heave. How is a time
series of 'heave' different from a time series of
height relative to some vertical datum? I've yet to
see a proposed definition that convinces me that this
is a uniquely different quantity.
Grace and peace,
Jim
On Fri, May 25, 2018 at 7:28 AM, Lowry, Roy K.
<[email protected]<mailto:[email protected]> wrote:
Dear All,
I agree with Nan that definitions of pitch roll
and yaw would improve the existing Standard Name
definitions. I also agree with using the existing
orientation Standard Names for ADCPs and that the
'platform' definition wording could make this
clearer. However, such an enhancements should be
submitted as a separate proposal and not be
considered as part of Steve's proposal.
Cheers, Roy.
----------------------------------------------------------------------
--
From: Nan Galbraith <[email protected]>
Sent: 25 May 2018 14:46
I'd really like to see pitch, roll and yaw
defined
in the CF standard name table; currently
the definitions only say 'Standard names for
platform describe the motion and orientation
of the vehicle from which observations are made
e.g. aeroplane, ship or satellite.'
Also, not to get too far into the weeds, but many
of the platform terms are important
for instruments like ADCPs, so I'd just like to
confirm that these definitions - and
the names themselves - can be used to describe
instruments, not just vehicles
'e.g. aeroplane, ship or satellite'. We already
use pitch roll and yaw for these
instruments on surface moorings, and I hope (and
assume) this is legal.
Thanks - Nan Galbraith
On 5/25/18 8:53 AM, Lowry, Roy K. wrote:
>
>
> Dear Steve,
>
>
> One of the reasons I was interested in your
definitions was your
> perspective on the datum (i.e. zero value) for
heave. The datum
> 'mean_sea_level' is well used in CF, but with
the definition 'time
> mean of sea surface elevation at a given
location over an arbitrary
> period sufficient to eliminate the tidal
signals.' This is obviously
> not appropriate for platform heave which
doesn't
take any account of
> the state of the tide and so I would exclude
'mean_sea_level' from the
> Standard Name.
>
>
> I think my preference would be to keep the term
'heave' as we already
> have 'pitch', 'yaw' and 'roll', giving:
>
>
> platform_heave (m)
>
>
> Standard names for platform describe the motion
and orientation of the
> vehicle from which observations are made e.g.
aeroplane, ship or
> satellite. "Heave" is a term used to describe
the vertical
> displacement of the platform above its position
when not moving.
>
>
> tendency_of_platform_heave (m s-1)
>
>
> Standard names for platform describe the motion
and orientation of the
> vehicle from which observations are made e.g.
aeroplane, ship or
> satellite. "Tendency_of_X" means derivative
of X
with respect to time.
> "Heave" is a term used to describe the vertical
displacement of the
> platform above its position when not moving.
>
>
> What do you think?
>
>
> Cheers, Roy.
