def read_binary_values(fh, pos=None, seg_y_type='int32', num_items=1, endian='>'):
"""Read a series of values from a binary file.
Args:
fh: A file-like-object open in binary mode.
seg_y_type: The SEG Y data type.
num_items: The number of items to be read.
Returns:
A sequence containing count items.
"""
ctype = SEG_Y_TYPE_TO_CTYPE[seg_y_type]
item_size = size_in_bytes(ctype)
block_size = item_size * num_items
fh.seek(pos, os.SEEK_SET)
buf = fh.read(block_size)
if len(buf) < block_size:
raise EOFError("{} bytes requested but only {} available".format(
block_size, len(buf)))
values = (unpack_ibm_floats(buf, num_items)
if ctype == 'ibm'
else unpack_values(buf, ctype, endian))
assert len(values) == num_items
return values
def trace_samples(self, trace_index, start=None, stop=None):
"""Read a specific trace_samples.
Args:
trace_index: An integer in the range zero to num_traces() - 1
start: Optional zero-based start sample index. The default
is to read from the first (i.e. zeroth) sample.
stop: Optional zero-based stop sample index. Following Python
slice convention this is one beyond the end.
Returns:
A sequence of numeric trace_samples samples.
Example:
first_trace_samples = segy_reader.trace_samples(0)
part_of_second_trace_samples = segy_reader.trace_samples(1, 1000, 2000)
"""
if not (0 <= trace_index < self.num_traces()):
raise ValueError("Trace index out of range.")
num_samples_in_trace = self.num_trace_samples(trace_index)
start_sample = start if start is not None else 0
stop_sample = stop if stop is not None else num_samples_in_trace
if not (0 <= stop_sample <= num_samples_in_trace):
raise ValueError(
"trace_samples(): stop value {} out of range 0 to {}".format(
stop, num_samples_in_trace))
if not (0 <= start_sample <= stop_sample):
raise ValueError(
"trace_samples(): start value {} out of range 0 to {}".format(
start, stop_sample))
dsf = self._binary_reel_header.data_sample_format
seg_y_type = DATA_SAMPLE_FORMAT_TO_SEG_Y_TYPE[dsf]
start_pos = (
self._trace_offset_catalog[trace_index] + TRACE_HEADER_NUM_BYTES +
start_sample * size_in_bytes(SEG_Y_TYPE_TO_CTYPE[seg_y_type]))
num_samples_to_read = stop_sample - start_sample
trace_values = read_binary_values(self._fh, start_pos, seg_y_type,
num_samples_to_read, self._endian)
return trace_values
def trace_samples(self, trace_index, start=None, stop=None):
"""Read a specific trace_samples.
Args:
trace_index: An integer in the range zero to num_traces() - 1
start: Optional zero-based start sample index. The default
is to read from the first (i.e. zeroth) sample.
stop: Optional zero-based stop sample index. Following Python
slice convention this is one beyond the end.
Returns:
A sequence of numeric trace_samples samples.
Example:
first_trace_samples = segy_reader.trace_samples(0)
part_of_second_trace_samples = segy_reader.trace_samples(1, 1000, 2000)
"""
if not (0 <= trace_index < self.num_traces()):
raise ValueError("Trace index out of range.")
num_samples_in_trace = self.num_trace_samples(trace_index)
start_sample = start if start is not None else 0
stop_sample = stop if stop is not None else num_samples_in_trace
if not (0 <= stop_sample <= num_samples_in_trace):
raise ValueError("trace_samples(): stop value {} out of range 0 to {}"
.format(stop, num_samples_in_trace))
if not (0 <= start_sample <= stop_sample):
raise ValueError("trace_samples(): start value {} out of range 0 to {}"
.format(start, stop_sample))
dsf = self._binary_reel_header.data_sample_format
seg_y_type = DATA_SAMPLE_FORMAT_TO_SEG_Y_TYPE[dsf]
start_pos = (self._trace_offset_catalog[trace_index]
+ TRACE_HEADER_NUM_BYTES
+ start_sample * size_in_bytes(SEG_Y_TYPE_TO_CTYPE[seg_y_type]))
num_samples_to_read = stop_sample - start_sample
trace_values = read_binary_values(
self._fh, start_pos, seg_y_type, num_samples_to_read, self._endian)
return trace_values
def read_binary_values(fh, pos=None, seg_y_type='int32', num_items=1, endian='>'):
"""Read a series of values from a binary file.
Args:
fh: A file-like-object open in binary mode.
pos: An optional file offset in bytes from the beginning from which
the data is to be read. If None, the current file position will
be used.
seg_y_type: The SEG Y data type.
num_items: The number of items to be read.
endian: '>' for big-endian data (the standard and default), '<'
for little-endian (non-standard)
Returns:
A sequence containing count items.
"""
ctype = SEG_Y_TYPE_TO_CTYPE[seg_y_type]
item_size = size_in_bytes(ctype)
block_size = item_size * num_items
pos = fh.tell() if pos is None else pos
fh.seek(pos, os.SEEK_SET)
buf = fh.read(block_size)
if len(buf) < block_size:
raise EOFError("{} bytes requested but only {} available when reading "
"from position {}".format(block_size, len(buf), pos))
values = (unpack_ibm_floats(buf, num_items)
if ctype == 'ibm'
else unpack_values(buf, ctype, endian))
assert len(values) == num_items
return values
def test_illegal_ctypes_raise_value_error(ctype):
assume(ctype not in LEGAL_CTYPES)
with raises(ValueError):
size_in_bytes(ctype)
def test_floats_are_four_bytes(ctype):
assert size_in_bytes(ctype) == 4
def test_bytes_are_one_byte(ctype):
assert size_in_bytes(ctype) == 1
def test_shorts_are_two_bytes(ctype):
assert size_in_bytes(ctype) == 2
def test_integers_are_four_bytes(ctype):
assert size_in_bytes(ctype) == 4
