def unpack_4byte_integer(file, count, endian='>'):
"""
Unpacks 4 byte integers.
"""
# Read as 4 byte integer so bit shifting works.
data = from_buffer(file.read(count * 4), dtype=np.int32)
# Swap the byte order if necessary.
if BYTEORDER != endian:
data = data.byteswap()
return data
def unpack_4byte_ibm(file, count, endian='>'):
"""
Unpacks 4 byte IBM floating points.
"""
# Read as 4 byte integer so bit shifting works.
data = from_buffer(file.read(count * 4), dtype=np.float32)
# Swap the byte order if necessary.
if BYTEORDER != endian:
data = data.byteswap()
length = len(data)
# Call the C code which transforms the data inplace.
clibsegy.ibm2ieee(data, length)
return data
def parse_next_trace(self):
"""
Parse the next trace in the trace pointer list and return a Trace
object.
"""
trace_descriptor_block = self.file_pointer.read(32)
# Check if the trace descriptor block id is valid.
if unpack(self.endian + b'H', trace_descriptor_block[0:2])[0] != \
0x4422:
msg = 'Invalid trace descriptor block id.'
raise SEG2InvalidFileError(msg)
size_of_this_block, = unpack_from(self.endian + b'H',
trace_descriptor_block, 2)
number_of_samples_in_data_block, = \
unpack_from(self.endian + b'L', trace_descriptor_block, 8)
data_format_code, = unpack_from(b'B', trace_descriptor_block, 12)
# Parse the data format code.
if data_format_code == 4:
dtype = self.endian + b'f4'
sample_size = 4
elif data_format_code == 5:
dtype = self.endian + b'f8'
sample_size = 8
elif data_format_code == 1:
dtype = self.endian + b'i2'
sample_size = 2
elif data_format_code == 2:
dtype = self.endian + b'i4'
sample_size = 4
elif data_format_code == 3:
dtype = self.endian + b'i2'
sample_size = 2.5
if number_of_samples_in_data_block % 4 != 0:
raise SEG2InvalidFileError(
'Data format code 3 requires that the number of samples '
'is divisible by 4, but sample count is %d' %
(number_of_samples_in_data_block, ))
else:
msg = 'Unrecognized data format code'
raise SEG2InvalidFileError(msg)
# The rest of the trace block is free form.
header = {}
header['seg2'] = AttribDict()
self.parse_free_form(self.file_pointer.read(size_of_this_block - 32),
header['seg2'])
header['delta'] = float(header['seg2']['SAMPLE_INTERVAL'])
# Set to the file's start time.
header['starttime'] = deepcopy(self.starttime)
if 'DELAY' in header['seg2']:
if float(header['seg2']['DELAY']) != 0:
msg = "Non-zero value found in Trace's 'DELAY' field. " + \
"This is not supported/tested yet and might lead " + \
"to a wrong starttime of the Trace. Please contact " + \
"the ObsPy developers with a sample file."
warnings.warn(msg)
if "DESCALING_FACTOR" in header["seg2"]:
header['calib'] = float(header['seg2']['DESCALING_FACTOR'])
# Unpack the data.
data = from_buffer(self.file_pointer.read(
int(number_of_samples_in_data_block * sample_size)),
dtype=dtype)
if data_format_code == 3:
# Convert one's complement to two's complement by adding one to
# negative numbers.
one_to_two = (data < 0)
# The first two bytes (1 word) of every 10 bytes (5 words) contains
# a 4-bit exponent for each of the 4 remaining 2-byte (int16)
# samples.
exponents = data[0::5].view(self.endian + b'u2')
result = np.empty(number_of_samples_in_data_block, dtype=np.int32)
# Apply the negative correction, then multiply by correct exponent.
result[0::4] = ((data[1::5] + one_to_two[1::5]) *
2**((exponents & 0x000f) >> 0))
result[1::4] = ((data[2::5] + one_to_two[2::5]) *
2**((exponents & 0x00f0) >> 4))
result[2::4] = ((data[3::5] + one_to_two[3::5]) *
2**((exponents & 0x0f00) >> 8))
result[3::4] = ((data[4::5] + one_to_two[4::5]) *
2**((exponents & 0xf000) >> 12))
data = result
# Integrate SEG2 file header into each trace header
tmp = self.stream.stats.seg2.copy()
tmp.update(header['seg2'])
header['seg2'] = tmp
return Trace(data=data, header=header)