# Thread: Rotation normal or reverse

Started: 2020-05-08 04:16:59
Last activity: 2020-05-08 15:21:56
Topics:
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

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

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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/ |
Unsubscribe: sac-help-unsubscribe<at>lists.ds.iris.edu

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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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