# [Met_help] [rt.rap.ucar.edu #47990] History for Axis angle in MODE

RAL HelpDesk {for Paul Oldenburg} met_help at ucar.edu
Fri Jul 22 13:49:12 MDT 2011

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Initial Request
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Hello,

I am working with MODE and have a question about how the attribute "Axis
Angle" is computed.  I see that it uses 3rd order moments.  What I am
wondering is if the axis angle is calculated using grid point distances or
earth distances?

Thank you,

Arin Peters

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Complete Ticket History
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Subject: Re: [rt.rap.ucar.edu #47990] Axis angle in MODE
From: Paul Oldenburg
Time: Thu Jun 30 13:22:28 2011

Arin,

All the calculations are done in grid coordinates.  The axis angle is
not actually calculated using 3rd order moments as
you mentioned.  The axis of a MODE object is determined using the
technique of principle components decomposition.  If
you have any other questions, please let us know.

Thanks,

Paul

On 06/30/2011 01:00 PM, RAL HelpDesk {for Arin Peters} wrote:
>
> Thu Jun 30 13:00:36 2011: Request 47990 was acted upon.
> Transaction: Ticket created by arinpeters at gmail.com
>        Queue: met_help
>      Subject: Axis angle in MODE
>        Owner: Nobody
>   Requestors: arinpeters at gmail.com
>       Status: new
>  Ticket <URL:
https://rt.rap.ucar.edu/rt/Ticket/Display.html?id=47990 >
>
>
> Hello,
>
> I am working with MODE and have a question about how the attribute
"Axis
> Angle" is computed.  I see that it uses 3rd order moments.  What I
am
> wondering is if the axis angle is calculated using grid point
distances or
> earth distances?
>
> Thank you,
>
> Arin Peters
>

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Subject: Axis angle in MODE
From: Arin Peters
Time: Sat Jul 02 16:41:58 2011

Paul,

Thank you for the response.  Thanks for correcting me on the 3rd order
moments...I mistyped and should have said 2nd order moments.  Anyway,
my
next question is do you have any documentation about the principle
components decomposition technique?  I would like to look over how it
is
done.

Thank you,

Arin

On Thu, Jun 30, 2011 at 2:22 PM, RAL HelpDesk {for Paul Oldenburg} <
met_help at ucar.edu> wrote:

> Arin,
>
> All the calculations are done in grid coordinates.  The axis angle
is not
> actually calculated using 3rd order moments as
> you mentioned.  The axis of a MODE object is determined using the
technique
> of principle components decomposition.  If
> you have any other questions, please let us know.
>
> Thanks,
>
> Paul
>
>
> On 06/30/2011 01:00 PM, RAL HelpDesk {for Arin Peters} wrote:
> >
> > Thu Jun 30 13:00:36 2011: Request 47990 was acted upon.
> > Transaction: Ticket created by arinpeters at gmail.com
> >        Queue: met_help
> >      Subject: Axis angle in MODE
> >        Owner: Nobody
> >   Requestors: arinpeters at gmail.com
> >       Status: new
> >  Ticket <URL:
https://rt.rap.ucar.edu/rt/Ticket/Display.html?id=47990 >
> >
> >
> > Hello,
> >
> > I am working with MODE and have a question about how the attribute
"Axis
> > Angle" is computed.  I see that it uses 3rd order moments.  What I
am
> > wondering is if the axis angle is calculated using grid point
distances
> or
> > earth distances?
> >
> > Thank you,
> >
> > Arin Peters
> >
>
>
>

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Subject: Re: [rt.rap.ucar.edu #47990] Axis angle in MODE
From: John Halley Gotway
Time: Mon Jul 04 09:23:59 2011

Hello Arin,

This is John - I work with Paul.  We actually do have about write-up
on
this posted on the MET website written by Randy Bullock.  I think you
win
the prize for being the first MET user to request it!  If you have
more

Here's the link to the documentation page (look for "Moments,
Centroid,
and Axis Angles"):
http://www.dtcenter.org/met/users/docs/overview.php

And here's the direct link to the PDF:
http://www.dtcenter.org/met/users/docs/write_ups/moments.pdf

Thanks,
John

>
> <URL: https://rt.rap.ucar.edu/rt/Ticket/Display.html?id=47990 >
>
> Paul,
>
> Thank you for the response.  Thanks for correcting me on the 3rd
order
> moments...I mistyped and should have said 2nd order moments.
Anyway, my
> next question is do you have any documentation about the principle
> components decomposition technique?  I would like to look over how
it is
> done.
>
> Thank you,
>
> Arin
>
> On Thu, Jun 30, 2011 at 2:22 PM, RAL HelpDesk {for Paul Oldenburg} <
> met_help at ucar.edu> wrote:
>
>> Arin,
>>
>> All the calculations are done in grid coordinates.  The axis angle
is
>> not
>> actually calculated using 3rd order moments as
>> you mentioned.  The axis of a MODE object is determined using the
>> technique
>> of principle components decomposition.  If
>> you have any other questions, please let us know.
>>
>> Thanks,
>>
>> Paul
>>
>>
>> On 06/30/2011 01:00 PM, RAL HelpDesk {for Arin Peters} wrote:
>> >
>> > Thu Jun 30 13:00:36 2011: Request 47990 was acted upon.
>> > Transaction: Ticket created by arinpeters at gmail.com
>> >        Queue: met_help
>> >      Subject: Axis angle in MODE
>> >        Owner: Nobody
>> >   Requestors: arinpeters at gmail.com
>> >       Status: new
>> >  Ticket <URL:
https://rt.rap.ucar.edu/rt/Ticket/Display.html?id=47990
>> >
>> >
>> >
>> > Hello,
>> >
>> > I am working with MODE and have a question about how the
attribute
>> "Axis
>> > Angle" is computed.  I see that it uses 3rd order moments.  What
I am
>> > wondering is if the axis angle is calculated using grid point
>> distances
>> or
>> > earth distances?
>> >
>> > Thank you,
>> >
>> > Arin Peters
>> >
>>
>>
>>
>

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