Re: [CF-metadata] Platform Heave

[Ethan Davis]

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  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  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 "anticloc

Re: [CF-metadata] Platform Heave

[Jim Biard]

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 > 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
  

Re: [CF-metadata] Platform Heave

[John Helly]

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  > 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
> directio

Re: [CF-metadata] Platform Heave

[Ethan Davis]

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  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

Re: [CF-metadata] Platform Heave

[Jim Biard]

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 sen