Hi All,
If the Station Coordinate headers (STLA STLO) and Epicenter Coordinate
headers (EVLA EVLO) are defined in a SAC file, SAC computes the
epicentral distance (DIST) automatically. I would like to know the
mathematical expression and the projection system SAC uses to compute
this distance. I will be really grateful if someone can provide a link
or a reference or the actual expression itself.
Thanks.
Avinash
If the Station Coordinate headers (STLA STLO) and Epicenter Coordinate
headers (EVLA EVLO) are defined in a SAC file, SAC computes the
epicentral distance (DIST) automatically. I would like to know the
mathematical expression and the projection system SAC uses to compute
this distance. I will be really grateful if someone can provide a link
or a reference or the actual expression itself.
Thanks.
Avinash

Hi Avinash,
I believe it uses the Vincenty's formula:
http://en.wikipedia.org/wiki/Vincenty's_formulae
Best,
Weisen
On Tue, Mar 25, 2014 at 5:53 PM, Avinash Nayak <avinash07guddu<at>gmail.com>wrote:
Hi All,

If the Station Coordinate headers (STLA STLO) and Epicenter Coordinate
headers (EVLA EVLO) are defined in a SAC file, SAC computes the
epicentral distance (DIST) automatically. I would like to know the
mathematical expression and the projection system SAC uses to compute
this distance. I will be really grateful if someone can provide a link
or a reference or the actual expression itself.
Thanks.
Avinash
_______________________________________________
sachelp mailing list
sachelp<at>iris.washington.edu
http://www.iris.washington.edu/mailman/listinfo/sachelp
Graduate Research Assistant
Center for Imaging the Earth's Interior, Department of Physics
University of Colorado at Boulder
http://ciei.colorado.edu/~weisen

Hi,
In my "old" manual i find:

Note: calculations of DIST, AZ, BAZ, and GCARC are based upon
the reference spheroid of 1968 and are defined by the major radius (RAD) and the flattening (FL). DIST is computed by Rudoe’s formula given in GEODESY, section 2.15(b).

But i do not check if it formula has been change in the last versions.
By the way:
I always ask me: what is the reason, why not use the WGS84 ellipsoid,
so, in this way SAC could be compatible with default GMT(4,5) ellipsoid.
Cheers,
* * * * * * * * * * * * * * * * * * * * * * *
Milton P. PLASENCIA LINARES
Centro di Ricerche Sismologiche (CRS)
OGS  Istituto Nazionale di Oceanografia e di Geofisica Sperimentale
Borgo Grotta Gigante 42/C
(34010) Sgonico  Trieste  Italia
Tel: +39 040 2140 141 (Udine)
Tel: +39 040 2140 256 (Trieste)
Cel.: +39 331 6481 935
Email: mplasencia<at>inogs.it
ASAIN (Antarctic Seismographic Argentinean Italian Network)
*********************************
On Mar 26, 2014, at 12:53 AM, Avinash Nayak <avinash07guddu<at>gmail.com> wrote:
Hi All,
If the Station Coordinate headers (STLA STLO) and Epicenter Coordinate
headers (EVLA EVLO) are defined in a SAC file, SAC computes the
epicentral distance (DIST) automatically. I would like to know the
mathematical expression and the projection system SAC uses to compute
this distance. I will be really grateful if someone can provide a link
or a reference or the actual expression itself.
Thanks.
Avinash
_______________________________________________
sachelp mailing list
sachelp<at>iris.washington.edu
http://www.iris.washington.edu/mailman/listinfo/sachelp

Milton,
We are still using Rudoe's Formula. Please see
http://www.iris.washington.edu/pipermail/sachelp/2013November/001592.html
We might change to a more robust formulation.
Changing the ellipsoid is not difficult and we have contemplated making this configurable (it will probably be done soon, maybe the next release).
Brian Savage
On Mar 26, 2014, at 2:28 AM, Milton Plasencia wrote:
Hi,
In my "old" manual i find:

Note: calculations of DIST, AZ, BAZ, and GCARC are based upon
the reference spheroid of 1968 and are defined by the major radius (RAD) and the flattening (FL). DIST is computed by Rudoe’s formula given in GEODESY, section 2.15(b).

But i do not check if it formula has been change in the last versions.
By the way:
I always ask me: what is the reason, why not use the WGS84 ellipsoid,
so, in this way SAC could be compatible with default GMT(4,5) ellipsoid.
Cheers,
* * * * * * * * * * * * * * * * * * * * * * *
Milton P. PLASENCIA LINARES
Centro di Ricerche Sismologiche (CRS)
OGS  Istituto Nazionale di Oceanografia e di Geofisica Sperimentale
Borgo Grotta Gigante 42/C
(34010) Sgonico  Trieste  Italia
Tel: +39 040 2140 141 (Udine)
Tel: +39 040 2140 256 (Trieste)
Cel.: +39 331 6481 935
Email: mplasencia<at>inogs.it
ASAIN (Antarctic Seismographic Argentinean Italian Network)
*********************************
On Mar 26, 2014, at 12:53 AM, Avinash Nayak <avinash07guddu<at>gmail.com> wrote:
Hi All,
_______________________________________________
If the Station Coordinate headers (STLA STLO) and Epicenter Coordinate
headers (EVLA EVLO) are defined in a SAC file, SAC computes the
epicentral distance (DIST) automatically. I would like to know the
mathematical expression and the projection system SAC uses to compute
this distance. I will be really grateful if someone can provide a link
or a reference or the actual expression itself.
Thanks.
Avinash
_______________________________________________
sachelp mailing list
sachelp<at>iris.washington.edu
http://www.iris.washington.edu/mailman/listinfo/sachelp
sachelp mailing list
sachelp<at>iris.washington.edu
http://www.iris.washington.edu/mailman/listinfo/sachelp

Brian,
Excellent news!!
I think it update will be very important for the SAC user community.
Cheers,
Milton P. Plasencia Linares
mpplasencia<at>gmail.com
On Mar 28, 2014, at 3:06 PM, Brian Savage <savage<at>uri.edu> wrote:
Milton,
We are still using Rudoe's Formula. Please see
http://www.iris.washington.edu/pipermail/sachelp/2013November/001592.html
We might change to a more robust formulation.
Changing the ellipsoid is not difficult and we have contemplated making this configurable (it will probably be done soon, maybe the next release).
Brian Savage
On Mar 26, 2014, at 2:28 AM, Milton Plasencia wrote:
Hi,
In my "old" manual i find:

Note: calculations of DIST, AZ, BAZ, and GCARC are based upon
the reference spheroid of 1968 and are defined by the major radius (RAD) and the flattening (FL). DIST is computed by Rudoe’s formula given in GEODESY, section 2.15(b).

But i do not check if it formula has been change in the last versions.
By the way:
I always ask me: what is the reason, why not use the WGS84 ellipsoid,
so, in this way SAC could be compatible with default GMT(4,5) ellipsoid.
Cheers,
* * * * * * * * * * * * * * * * * * * * * * *
Milton P. PLASENCIA LINARES
Centro di Ricerche Sismologiche (CRS)
OGS  Istituto Nazionale di Oceanografia e di Geofisica Sperimentale
Borgo Grotta Gigante 42/C
(34010) Sgonico  Trieste  Italia
Tel: +39 040 2140 141 (Udine)
Tel: +39 040 2140 256 (Trieste)
Cel.: +39 331 6481 935
Email: mplasencia<at>inogs.it
ASAIN (Antarctic Seismographic Argentinean Italian Network)
*********************************
On Mar 26, 2014, at 12:53 AM, Avinash Nayak <avinash07guddu<at>gmail.com> wrote:
Hi All,
_______________________________________________
If the Station Coordinate headers (STLA STLO) and Epicenter Coordinate
headers (EVLA EVLO) are defined in a SAC file, SAC computes the
epicentral distance (DIST) automatically. I would like to know the
mathematical expression and the projection system SAC uses to compute
this distance. I will be really grateful if someone can provide a link
or a reference or the actual expression itself.
Thanks.
Avinash
_______________________________________________
sachelp mailing list
sachelp<at>iris.washington.edu
http://www.iris.washington.edu/mailman/listinfo/sachelp
sachelp mailing list
sachelp<at>iris.washington.edu
http://www.iris.washington.edu/mailman/listinfo/sachelp

