Thread: LEVEN = TRUE but IrisFetch (Matlab) says "Data is unevenly spaced"

Started: 2022-05-03 18:47:26
Last activity: 2022-05-04 08:56:03
Topics: SAC Help
I converted some SAC files that were originally V6 (NVHDR = 6 ) to V7 (NVHDR = 7). I then did a transfer to produce a velocity time-series file. The original and product files are now in V7.

When I try to load either V7 sac file into Matlab, it will not load any data and returns:
Error using irisFetch/read_sac_in (line 2485)
IRISFETCH:read_sac_in - Data is unevenly spaced.

However, when I open the header of either V7 file,
LEVEN = TRUE
And the SAC manual says "LEVEN TRUE if data set is evenly spaced"

I do not have a problem loading the V6 sac files into Matlab. I do not get this error message in Matlab. But, as far as I understand, I need to have it in V7 for the sake of the accuracy of my time values.

How do I resolve this?
  • Dear All -

    From reading the Matlab code, this is a bug that should be reported to the maintainers at IRIS.

    Briefly, the code cannot handle V7 SAC files properly; if the version number is not 6, the code assumes it is just a byte-swapped SAC file. It does not recognize that V7 headers exist.

    On 3 May 2022, at 20:02, Loring Schaible (via IRIS) <sac-help-bounce<at>lists.ds.iris.edu> wrote:

    I converted some SAC files that were originally V6 (NVHDR = 6 ) to V7 (NVHDR = 7). I then did a transfer to produce a velocity time-series file. The original and product files are now in V7.

    When I try to load either V7 sac file into Matlab, it will not load any data and returns:
    Error using irisFetch/read_sac_in (line 2485)
    IRISFETCH:read_sac_in - Data is unevenly spaced.

    However, when I open the header of either V7 file,
    LEVEN = TRUE
    And the SAC manual says "LEVEN TRUE if data set is evenly spaced"

    I do not have a problem loading the V6 sac files into Matlab. I do not get this error message in Matlab. But, as far as I understand, I need to have it in V7 for the sake of the accuracy of my time values.

    How do I resolve this?

    ----------------------
    SAC Help
    Topic home: http://ds.iris.edu/message-center/topic/sac-help/ | Unsubscribe: sac-help-unsubscribe<at>lists.ds.iris.edu

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    George Helffrich
    george<at>elsi.jp



    • Hi Loring and George-

      Thank you for detecting this bug. Please file an Issue ticket in our GitHub project so we can investigate this further.

      https://github.com/iris-edu/irisFetch-matlab

      Regards,

      -Rob


      On May 3, 2022, at 6:13 PM, George Helffrich (via IRIS) <sac-help-bounce<at>lists.ds.iris.edu> wrote:

      Dear All -

      From reading the Matlab code, this is a bug that should be reported to the maintainers at IRIS.

      Briefly, the code cannot handle V7 SAC files properly; if the version number is not 6, the code assumes it is just a byte-swapped SAC file. It does not recognize that V7 headers exist.

      On 3 May 2022, at 20:02, Loring Schaible (via IRIS) <sac-help-bounce<at>lists.ds.iris.edu <sac-help-bounce<at>lists.ds.iris.edu>> wrote:

      I converted some SAC files that were originally V6 (NVHDR = 6 ) to V7 (NVHDR = 7). I then did a transfer to produce a velocity time-series file. The original and product files are now in V7.

      When I try to load either V7 sac file into Matlab, it will not load any data and returns:
      Error using irisFetch/read_sac_in (line 2485)
      IRISFETCH:read_sac_in - Data is unevenly spaced.

      However, when I open the header of either V7 file,
      LEVEN = TRUE
      And the SAC manual says "LEVEN TRUE if data set is evenly spaced"

      I do not have a problem loading the V6 sac files into Matlab. I do not get this error message in Matlab. But, as far as I understand, I need to have it in V7 for the sake of the accuracy of my time values.

      How do I resolve this?

      ----------------------
      SAC Help
      Topic home: http://ds.iris.edu/message-center/topic/sac-help/ | Unsubscribe: sac-help-unsubscribe<at>lists.ds.iris.edu <sac-help-unsubscribe<at>lists.ds.iris.edu>

      Sent from the IRIS Message Center (http://ds.iris.edu/message-center/)
      Update subscription preferences at http://ds.iris.edu/account/profile/



      George Helffrich
      george<at>elsi.jp <george<at>elsi.jp>

      ----------------------
      SAC Help
      Topic home: http://ds.iris.edu/message-center/topic/sac-help/ | Unsubscribe: sac-help-unsubscribe<at>lists.ds.iris.edu

      Sent from the IRIS Message Center (http://ds.iris.edu/message-center/)
      Update subscription preferences at http://ds.iris.edu/account/profile/


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