core.py

#!/usr/bin/env python
# ----------------------------------------------------------------------
# Filename: core.py
#  Purpose: Python Class for transforming seismograms to audio WAV files
#   Author: Moritz Beyreuther
#    Email: moritz.beyreuther@geophysik.uni-muenchen.de
#
# Copyright (C) 2009-2012 Moritz Beyreuther
# ------------------------------------------------------------------------
"""
WAV bindings to ObsPy core module.

:copyright:
    The ObsPy Development Team (devs@obspy.org)
:license:
    GNU Lesser General Public License, Version 3
    (https://www.gnu.org/copyleft/lesser.html)
"""
from __future__ import (absolute_import, division, print_function,
                        unicode_literals)
from future.builtins import *  # NOQA
from future.utils import native_str

import os
import wave

import numpy as np

from obspy import Stream, Trace
from obspy.core.compatibility import from_buffer


# WAVE data format is unsigned char up to 8bit, and signed int
# for the remaining.
WIDTH2DTYPE = {
    1: native_str('<u1'),  # unsigned char
    2: native_str('<i2'),  # signed short int
    4: native_str('<i4'),  # signed int (int32)
}


def _is_wav(filename):
    """
    Checks whether a file is a audio WAV file or not.

    :type filename: str
    :param filename: Name of the audio WAV file to be checked.
    :rtype: bool
    :return: ``True`` if a WAV file.

    .. rubric:: Example

    >>> _is_wav("/path/to/3cssan.near.8.1.RNON.wav")  #doctest: +SKIP
    True
    """
    try:
        fh = wave.open(filename, 'rb')
        try:
            (_nchannel, width, _rate, _len, _comptype, _compname) = \
                fh.getparams()
        finally:
            fh.close()
    except Exception:
        return False
    if width in [1, 2, 4]:
        return True
    return False


def _read_wav(filename, headonly=False, **kwargs):  # @UnusedVariable
    """
    Reads a audio WAV file and returns an ObsPy Stream object.

    Currently supports uncompressed unsigned char and short integer and
    integer data values. This should cover most WAV files.

    .. warning::
        This function should NOT be called directly, it registers via the
        ObsPy :func:`~obspy.core.stream.read` function, call this instead.

    :type filename: str
    :param filename: Audio WAV file to be read.
    :rtype: :class:`~obspy.core.stream.Stream`
    :return: A ObsPy Stream object.

    .. rubric:: Example

    >>> from obspy import read
    >>> st = read("/path/to/3cssan.near.8.1.RNON.wav")
    >>> print(st) #doctest: +NORMALIZE_WHITESPACE
    1 Trace(s) in Stream:
    ... | 1970-01-01T00:00:00.000000Z - 1970-01-01T00:00:00.371143Z
    | 7000.0 Hz, 2599 samples
    """
    # read WAV file
    fh = wave.open(filename, 'rb')
    try:
        # header information
        (_nchannel, width, rate, length, _comptype, _compname) = fh.getparams()
        header = {'sampling_rate': rate, 'npts': length}
        if headonly:
            return Stream([Trace(header=header)])
        if width not in WIDTH2DTYPE.keys():
            msg = "Unsupported Format Type, word width %dbytes" % width
            raise TypeError(msg)
        data = from_buffer(fh.readframes(length), dtype=WIDTH2DTYPE[width])
    finally:
        fh.close()
    return Stream([Trace(header=header, data=data)])


def _write_wav(stream, filename, framerate=7000, rescale=False, width=None,
               **kwargs):  # @UnusedVariable
    """
    Writes a audio WAV file from given ObsPy Stream object. The seismogram is
    squeezed to audible frequencies.

    The generated WAV sound file is as a result really short. The data
    are written uncompressed as signed 4-byte integers.

    .. warning::
        This function should NOT be called directly, it registers via the
        the :meth:`~obspy.core.stream.Stream.write` method of an
        ObsPy :class:`~obspy.core.stream.Stream` object, call this instead.

    :type stream: :class:`~obspy.core.stream.Stream`
    :param stream: The ObsPy Stream object to write.
    :type filename: str
    :param filename: Name of the audio WAV file to write.
    :type framerate: int, optional
    :param framerate: Sample rate of WAV file to use. This this will squeeze
        the seismogram (default is 7000).
    :type rescale: bool, optional
    :param rescale: Maximum to maximal representable number
    :type width: int, optional
    :param width: dtype to write, 1 for '<u1', 2 for '<i2' or 4 for '<i4'.
        tries to autodetect width from data, uses 4 otherwise
    """
    i = 0
    base, ext = os.path.splitext(filename)
    if width not in WIDTH2DTYPE.keys() and width is not None:
        raise TypeError("Unsupported Format Type, word width %dbytes" % width)
    for trace in stream:
        # try to autodetect width from data, see #791
        if width is None:
            if trace.data.dtype.str[-2:] in ['u1', 'i2', 'i4']:
                tr_width = int(trace.data.dtype.str[-1])
            else:
                tr_width = 4
        else:
            tr_width = width
        # write WAV file
        if len(stream) >= 2:
            filename = "%s%03d%s" % (base, i, ext)
        w = wave.open(filename, 'wb')
        try:
            trace.stats.npts = len(trace.data)
            # (nchannels, sampwidth, framerate, nframes, comptype, compname)
            w.setparams((1, tr_width, framerate, trace.stats.npts, 'NONE',
                         'not compressed'))
            data = trace.data
            dtype = WIDTH2DTYPE[tr_width]
            if rescale:
                # optimal scale, account for +/- and the zero
                maxint = 2 ** (width * 8 - 1) - 1
                # upcast for following rescaling
                data = data.astype(np.float64)
                data = data / abs(data).max() * maxint
            data = np.require(data, dtype=dtype)
            w.writeframes(data.tostring())
        finally:
            w.close()
        i += 1


if __name__ == '__main__':
    import doctest
    doctest.testmod(exclude_empty=True)