Thread: Rotation normal or reverse

Started: 2020-05-08 04:16:59
Last activity: 2020-05-08 15:21:56
Topics: SAC Help
sanjay Singh Negi
2020-05-08 04:16:59
Hi,
What algorithm is followed when we use sac rotate, reverse or normal

For e.g., in sac the difference between

rotate to gcp normal

and

rotate to gcp reverse

Thank you

Regards
Sanjay

  • Milton Plasencia
    2020-05-08 00:57:03
    Hi,

    I invite you to see the information on sac help,

    sac> help rotate

    INPUT

    -----

    :TO GCP: Rotate to the "great circle path". Both components must be

    horizontals. The station and event coordinates header fields must

    be defined.


    :TO v: Rotate to the angle v (degrees). Both components must be

    horizontals.


    :THROUGH v: Rotate through the angle v in degrees. One component may

    be vertical.


    :NORMAL: Output (horizontal) components with the second leading the
    first by 90 degrees


    :REVERSED: Output (horizontal) components with the second lagging the
    first by 90 degrees.


    DEFAULT VALUES

    --------------

    ::


    ROTATE TO GCP NORMAL


    HTH,

    Milton

    ----------------------------
    Milton P. Plasencia Linares
    mpplasencia@ <mplasencia<at>inogs.it>gmail.com



    On Fri, May 8, 2020 at 12:53 AM sanjay Singh Negi (via IRIS) <
    sac-help<at>lists.ds.iris.edu> wrote:

    Hi,
    What algorithm is followed when we use sac rotate, reverse or normal

    For e.g., in sac the difference between

    rotate to gcp normal

    and

    rotate to gcp reverse

    Thank you

    Regards
    Sanjay




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    • Arthur Snoke
      2020-05-07 23:16:21
      If North is zero degrees, East is 90 degrees, so East leads North by 90 degrees.

      There is some confusion with the conventions because  SAC defines
      upward-vertical as positive, while others (e.g., Kennett) define
      downward-vertical as positive.  So for the SAC convention, Vertical, North, and
      East is a left-handed coordinate system.


      On 5/7/20 7:34 PM, Milton Plasencia (via IRIS) wrote:
      Hi,

      I invite you to see the information on sac help,

      sac> help rotate

      INPUT

      -----

      :TO GCP:  Rotate to the "great circle path".  Both components must be

      horizontals.  The station and event coordinates header fields must

      be defined.


      :TO v:  Rotate to the angle v (degrees).  Both components must be

      horizontals.


      :THROUGH v:  Rotate through the angle v in degrees.  One component may

      be vertical.


      :NORMAL:  Output (horizontal) components with the second leading the first by
      90 degrees


      :REVERSED:  Output (horizontal) components with the second lagging the first
      by 90 degrees.


      DEFAULT VALUES

      --------------

      ::


      ROTATE TO GCP NORMAL



      HTH,

      Milton

      ----------------------------
      Milton P. Plasencia Linares
      mpplasencia@ <mplasencia<at>inogs.it>gmail.com http://gmail.com



      On Fri, May 8, 2020 at 12:53 AM sanjay Singh Negi (via IRIS)
      <sac-help<at>lists.ds.iris.edu <sac-help<at>lists.ds.iris.edu>> wrote:

      Hi,
      What algorithm is followed when we use sac rotate, reverse or normal

      For e.g., in sac the difference between

      rotate to gcp normal

      and

      rotate to gcp reverse

      Thank you

      Regards
      Sanjay




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      • sanjay Singh Negi
        2020-05-08 15:21:56
        You are absolutely correct. However, we know that for the right-handed
        system,
        where east component lags behind the north component by 90 deg, we use
        reverse option.
        Actually, after reading the rotate help section, I was able to clear that
        the for reverse case, changes are applied in the output directions.
        Earlier, I was confused that whether the coordinate system is changed while
        rotation or not?
        It was really very helpful.
        Thank you,
        Regards
        Sanjay

        On Fri, May 8, 2020 at 8:51 AM Arthur Snoke (via IRIS) <
        sac-help<at>lists.ds.iris.edu> wrote:

        If North is zero degrees, East is 90 degrees, so East leads North by 90
        degrees.

        There is some confusion with the conventions because SAC defines
        upward-vertical as positive, while others (e.g., Kennett) define
        downward-vertical as positive. So for the SAC convention, Vertical,
        North, and
        East is a left-handed coordinate system.


        On 5/7/20 7:34 PM, Milton Plasencia (via IRIS) wrote:
        Hi,

        I invite you to see the information on sac help,

        sac> help rotate

        INPUT

        -----

        :TO GCP: Rotate to the "great circle path". Both components must be

        horizontals. The station and event coordinates header fields must

        be defined.


        :TO v: Rotate to the angle v (degrees). Both components must be

        horizontals.


        :THROUGH v: Rotate through the angle v in degrees. One component may

        be vertical.


        :NORMAL: Output (horizontal) components with the second leading the
        first by
        90 degrees


        :REVERSED: Output (horizontal) components with the second lagging the
        first
        by 90 degrees.


        DEFAULT VALUES

        --------------

        ::


        ROTATE TO GCP NORMAL



        HTH,

        Milton

        ----------------------------
        Milton P. Plasencia Linares
        mpplasencia@ <mplasencia<at>inogs.it>gmail.com http://gmail.com



        On Fri, May 8, 2020 at 12:53 AM sanjay Singh Negi (via IRIS)
        <sac-help<at>lists.ds.iris.edu <sac-help<at>lists.ds.iris.edu>> wrote:

        Hi,
        What algorithm is followed when we use sac rotate, reverse or normal

        For e.g., in sac the difference between

        rotate to gcp normal

        and

        rotate to gcp reverse

        Thank you

        Regards
        Sanjay




        ----------------------
        SAC Help
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        Unsubscribe: sac-help-unsubscribe<at>lists.ds.iris.edu
        <sac-help-unsubscribe<at>lists.ds.iris.edu>

        Sent from the IRIS Message Center (
        http://ds.iris.edu/message-center/)
        Update subscription preferences at
        http://ds.iris.edu/account/profile/


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        --



        Sanjay Singh Negi
        Alternate Email: sasnegi85<at>gmail.com

        Contact No.- +91-9536145596

    • sanjay Singh Negi
      2020-05-08 05:12:37
      Thanks for the information. As I have already gone through the information,
      but I need an understanding as to what is going behind the command.
      Regars

      On Fri, May 8, 2020, 05:08 Milton Plasencia (via IRIS) <
      sac-help<at>lists.ds.iris.edu> wrote:

      Hi,

      I invite you to see the information on sac help,

      sac> help rotate

      INPUT

      -----

      :TO GCP: Rotate to the "great circle path". Both components must be

      horizontals. The station and event coordinates header fields must

      be defined.


      :TO v: Rotate to the angle v (degrees). Both components must be

      horizontals.


      :THROUGH v: Rotate through the angle v in degrees. One component may

      be vertical.


      :NORMAL: Output (horizontal) components with the second leading the
      first by 90 degrees


      :REVERSED: Output (horizontal) components with the second lagging the
      first by 90 degrees.


      DEFAULT VALUES

      --------------

      ::


      ROTATE TO GCP NORMAL


      HTH,

      Milton

      ----------------------------
      Milton P. Plasencia Linares
      mpplasencia@ <mplasencia<at>inogs.it>gmail.com



      On Fri, May 8, 2020 at 12:53 AM sanjay Singh Negi (via IRIS) <
      sac-help<at>lists.ds.iris.edu> wrote:

      Hi,
      What algorithm is followed when we use sac rotate, reverse or normal

      For e.g., in sac the difference between

      rotate to gcp normal

      and

      rotate to gcp reverse

      Thank you

      Regards
      Sanjay




      ----------------------
      SAC Help
      Topic home: http://ds.iris.edu/message-center/topic/sac-help/ |
      Unsubscribe: sac-help-unsubscribe<at>lists.ds.iris.edu

      Sent from the IRIS Message Center (http://ds.iris.edu/message-center/)
      Update subscription preferences at http://ds.iris.edu/account/profile/


      ----------------------
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    • sanjay Singh Negi
      2020-05-08 15:01:59
      Thank you Milton,
      I went through the help section.
      I now understand that the output directions are changed when we use the
      reverse option in rotating the seismogram.
      It was really very helpful.
      Thank you,
      Regards
      Sanjay

      On Fri, May 8, 2020 at 5:08 AM Milton Plasencia (via IRIS) <
      sac-help<at>lists.ds.iris.edu> wrote:

      Hi,

      I invite you to see the information on sac help,

      sac> help rotate

      INPUT

      -----

      :TO GCP: Rotate to the "great circle path". Both components must be

      horizontals. The station and event coordinates header fields must

      be defined.


      :TO v: Rotate to the angle v (degrees). Both components must be

      horizontals.


      :THROUGH v: Rotate through the angle v in degrees. One component may

      be vertical.


      :NORMAL: Output (horizontal) components with the second leading the
      first by 90 degrees


      :REVERSED: Output (horizontal) components with the second lagging the
      first by 90 degrees.


      DEFAULT VALUES

      --------------

      ::


      ROTATE TO GCP NORMAL


      HTH,

      Milton

      ----------------------------
      Milton P. Plasencia Linares
      mpplasencia@ <mplasencia<at>inogs.it>gmail.com



      On Fri, May 8, 2020 at 12:53 AM sanjay Singh Negi (via IRIS) <
      sac-help<at>lists.ds.iris.edu> wrote:

      Hi,
      What algorithm is followed when we use sac rotate, reverse or normal

      For e.g., in sac the difference between

      rotate to gcp normal

      and

      rotate to gcp reverse

      Thank you

      Regards
      Sanjay




      ----------------------
      SAC Help
      Topic home: http://ds.iris.edu/message-center/topic/sac-help/ |
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      Update subscription preferences at http://ds.iris.edu/account/profile/


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      --



      Sanjay Singh Negi
      Alternate Email: sasnegi85<at>gmail.com

      Contact No.- +91-9536145596

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