Thread: Re: sac-help Digest, Vol 29, Issue 4

Started: 2007-11-28 22:51:09
Last activity: 2007-11-28 22:51:09
Topics: SAC Help
Robert Herrmann
2007-11-28 22:51:09
sac-help-request<at>iris.washington.edu wrote:

Tim: I do not know if this response will get back to the mailing list -
so you get a copy

If the data stream should be modified to have doubles for the data, we
should also consider doubles for the SAC float header values - One
CANNOT pick time correctly at 23:59:59 for 200 Hz data sets (I know this
is extreme) is the continuous data stream starts at 00:00:00 - the
seven digit accuracy of floating point is exceeded

One would just need to redefine a new header version - I believe tha
tthe current header is at version 7

Given a define change, gsac would have it implemented in about one hour.
Internally gsac uses doubles for the float header values.


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Today's Topics:

1. Double Precision (Tim Ahern)


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

Message: 1
Date: Wed, 28 Nov 2007 11:41:39 -0800
From: Tim Ahern <tim<at>iris.washington.edu>
Subject: [SAC-HELP] Double Precision
To: sac-help<at>iris.washington.edu
Cc: Doug Neuhauser <doug<at>seismo.berkeley.edu>, Robert Uhrhammer
<bob<at>seismo.berkeley.edu>, Chris Laughbon <chris<at>iris.washington.edu>,
Charley Weiland <cweiland<at>stanford.edu>
Message-ID: <6741618B-B4D7-426A-BA46-F2294E89B7D1<at>iris.washington.edu>
Content-Type: text/plain; charset="us-ascii"

Greetings

We have a question for the SAC users group. Recently a need to
support double precision floating point for data in SEED format has
been identified.
While SEED itself can support this, the problem comes with possible
output formats the rdseed program should support. The most widely used
format is SAC format in our estimation.

Our question is, is it possible for SAC to support double precision
floating point values without loosing precision? Would it be
extremely difficult to
add double precision support for SAC? Even if SAC can not support
the format, would it make sense to have a double precision version of
the SAC Format, if
you understand what I mean by that.

One further question is, assuming that SAC and SAC format are not
ready for double precision and it would be difficult to support it...
what new format do you think we might consider supporting as an
output format for rdseed? Do any of you have suggestions as to
possible ways to deal with double precision floats as an output
format?

Thanks for any help you can provide us.

Cheers
Tim


Program Manager, IRIS Data Management System
IRIS DMC
1408 NE 45th Street #201
Seattle, WA 98105

(206)547-0393 x118
(206) 547-1093 FAX


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End of sac-help Digest, Vol 29, Issue 4
***************************************



--
Robert B. Herrmann
Otto W. Nuttli Professor of Geophysics
Department of Earth and Atmospheric Sciences
Saint Louis University
O'Neil Hall, Room 203
3642 Lindell Boulevard
St. Louis, MO 63108

TEL: 314 977 3120
FAX: 314 977 3117
Email: rbh<at>eas.slu.edu


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