ObsPy: Save Stream as SAC files

[seisman]

We can use Trace.write to save traces into SAC files, but the SAC files don't have event and station information. Below is codes that I've used for some while to save SAC files that have event and station information. I think it's useful and should be documented.

    Path(f"SAC/{ev.id}").mkdir(parents=True, exist_ok=True)
    for tr in st:
        sac = SACTrace.from_obspy_trace(tr)

        # set event information
        sac.evla = ev.latitude
        sac.evlo = ev.longitude
        sac.evdp = ev.depth
        sac.mag = ev.magnitude
        sac.reftime = ev.origin
        sac.o = 0.0
        sac.iztype = "io"

        # set station information
        coord = inv.get_coordinates(tr.id, datetime=ev.origin)
        sac.stla = coord["latitude"]
        sac.stlo = coord["longitude"]
        sac.stel = coord["elevation"]
        sac.stdp = coord["local_depth"]

        # set channel orientation
        orient = inv.get_orientation(tr.id, datetime=ev.origin)
        # Need to cautious with the different definitions of 'dip'
        # In ObsPy, 'dip' is degrees, down from horizontal [-90, 90]
        # In SAC, 'dip' is degrees, down from vertical-up [0, 180]
        sac.cmpinc = orient["dip"] + 90.0
        sac.cmpaz = orient["azimuth"]

        # set SAC header
        sac.lcalda = True  # calculate distance, azimuth and back-azimuth in saving
        print(f"SAC/{ev.id}/{tr.id}.SAC")
        sac.write(f"SAC/{ev.id}/{tr.id}.SAC")

Code from https://github.com/seisman/DDRelocator/blob/main/examples/ex2/process_data.py