[SAC-HELP] doubles in sac

Brian Savage savage at uri.edu
Thu Nov 29 08:28:21 PST 2007


All,

I am shifting this conversation over to sac-dev

Cheers,
Brian

On Nov 29, 2007, at  7:49 AM , Arthur Snoke wrote:

> I used the wrong address for the sac-help listserv.
>
> ---------- Forwarded message ----------
> Date: Wed, 28 Nov 2007 22:49:36 -0500 (EST)
> From: Arthur Snoke <snoke at vt.edu>
> To: Tim Ahern <tim at iris.washington.edu>, Brian Savage  
> <savage at uri.edu>,
>     Robert B. Herrmann <rbh at eas.slu.edu>
> Cc: sac-help-request at iris.washington.edu
> Subject: Re: [SAC-HELP] doubles in sac
>
> Tim and others,
>
> Bob touched on what I think is the biggest problem in modifying  
> sac: the header is fixed in length so one could not easily double  
> all the floats.
>
> The simplest interim solution as I see it that would allow sac to  
> continue to live is to have rdseed spew out single precision to a  
> sac format. Except for timing as in Bob's example or in very high  
> sample rates in general, where are doubles needed?
>
> Arthur
>
> On Wed, 28 Nov 2007, Robert B. Herrmann wrote:
>
>> 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.
>>> 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>
>>> 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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