[SAC-HELP] doubles in sac

[Arthur Snoke]

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