Relationship to ObsPy¶

PySAC is largely re-written from the obspy.io.sac module, with the intention of eventually replacing it.

Why a re-write?¶

The sacio module underlying ObsPy's SAC handling was sometimes hard to follow, as it has a long inheritance, which made it hard to track down issues or make fixes. This re-write attempts to make the SAC plugin easier to understand and maintain, as well as offer some potential improvements.

Improve maintainability.¶

I've split out the header specification (header.py), the low-level array-based SAC file I/O (arrayio.py), and the object-oriented interface (sactrace.py), whereas it was previously all within one sacio.py module. I hope that the flow of how each plugs into the other is clear, so that bug tracking is straight-forward, and that hacking on one aspect of SAC handling is not cluttered/distracted by another.

Expand support for round-trip SAC file processing¶

This rewrite attempts to improve support for a common work flow: read one or more SAC files into ObsPy, do some processing, then (over)write them back as SAC files that look mostly like the originals. Previously, ObsPy Traces written to SAC files wrote only files based on the first sample time (iztype 9/'ib'). In util.py:obspy_to_sac_header of this module, if an old tr.stats.sac SAC header is found, the iztype and reference "nz" times are used and kept, and the "b" and "e" times of the Trace being written are adjusted according to this reference time. This preserves the absolute reference of any relative time headers, like t0-t9, carried from the old SAC header into the new file. This can only be done if SAC to Trace conversion preserves these "nz" time headers, which is possible with the current debug_headers=True flag.