[SAC-HELP] Re: sac-help Digest, Vol 29, Issue 4

[Robert B. Herrmann]

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:
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>    1.  Double Precision (Tim Ahern)
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> ----------------------------------------------------------------------
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> 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
>
>
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-- 
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