Thread: Double Precision

Started: 2007-11-28 19:41:39
Last activity: 2007-11-29 15:40:59
Topics: SAC Help
Tim Ahern
Double Precision
2007-11-28 19:41:39
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



  • Peter Goldstein
    Re: Double Precision
    2007-11-29 04:02:44


    One approach that might allow for a quick test would be to redefine
    the float type to be the same as a double and then go in and find the
    places were offsets are hardwired in bytes, e.g., some of the include
    files. I'm not sure how long this would take and I may be forgetting
    something fundamental about sac that would preclude this.

    Cheers,

    Peter


    At 11:41 AM 11/28/2007, 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
    1408 NE 45th Street #201
    Seattle, WA 98105

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


    _______________________________________________
    sac-help mailing list
    sac-help<at>iris.washington.edu
    http://www.iris.washington.edu/mailman/listinfo/sac-help

  • George Helffrich
    Re: Double Precision
    2007-11-29 15:40:59
    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
    1408 NE 45th Street #201
    Seattle, WA  98105

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



    _______________________________________________
    sac-help mailing list
    sac-help<at>iris.washington.edu
    http://www.iris.washington.edu/mailman/listinfo/sac-help

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



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