[SAC-HELP] Double Precision

[George Helffrich]

Dear Tim -

	I would be helpful to know how the need for double precision floats 
arises.  Bob Herrman makes the point that some time calculations are 
better done with more floating point significant figures.  However 
today's seismic datalogger makers are happy putting out data as 
integers with 31 bit dynamic range.

	Would your needs be satisfied with a signed integer datatype in SAC 
rather than double precision float?

	My own gut feeling is that handling double precision floating point 
would be hard to do with SAC's present structure.  You could probably 
bodge together a version that would read a double precision file, do 
calculations internally in single precision, and write out double.  
Whether this is satisfactory depends on your intended use, however.

On 28 Nov 2007, at 19:41, Tim Ahern wrote:

>  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
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								George Helffrich
								george at geology.bristol.ac.uk