# http://pyrocko.org - GPLv3
#
# The Pyrocko Developers, 21st Century
# ---|P------/S----------~Lg----------
from __future__ import division, absolute_import
from builtins import range
import numpy as num
import struct
import calendar
from pyrocko import trace
from .io_common import FileLoadError
[docs]def ibm2ieee(ibm):
"""
Converts an IBM floating point number into IEEE format.
:param: ibm - 32 bit unsigned integer: unpack('>L', f.read(4))
"""
if ibm == 0:
return 0.0
sign = ibm >> 31 & 0x01
exponent = ibm >> 24 & 0x7f
mantissa = (ibm & 0x00ffffff) / float(pow(2, 24))
print('x', sign, exponent - 64, mantissa)
return (1 - 2 * sign) * mantissa * float(pow(16, exponent - 64))
[docs]def unpack_ibm_f4(data):
ibm = num.fromstring(data, dtype='>u4').astype(num.int32)
sign = (ibm >> 31) & 0x01
exponent = (ibm >> 24) & 0x7f
mantissa = (ibm & 0x00ffffff) / float(pow(2, 24))
xxx = (1 - 2 * sign) * mantissa * (16.0 ** (exponent - 64))\
.astype(num.float)
# for i in range(len(data)/4):
# yyy = ibm2ieee(struct.unpack('>L', data[i*4:(i+1)*4])[0])
# print('y', sign[i], exponent[i] - 64, mantissa[i])
# print(xxx[i], yyy)
# if xxx[i] != yyy:
# sys.exit()
# print
return xxx
[docs]class SEGYError(Exception):
pass
[docs]def iload(filename, load_data, endianness='>'):
'''Read SEGY file.
filename -- Name of SEGY file.
load_data -- If True, the data is read, otherwise only read headers.
'''
endianness = endianness
nbth = 3200
nbbh = 400
nbthx = 3200
nbtrh = 240
try:
f = open(filename, 'rb')
textual_file_header = f.read(nbth)
if len(textual_file_header) != nbth:
raise SEGYError('incomplete textual file header')
binary_file_header = f.read(nbbh)
if len(binary_file_header) != nbbh:
raise SEGYError('incomplete binary file header')
line_number = struct.unpack(endianness+'1I', binary_file_header[4:8])
hvals = struct.unpack(endianness+'24H', binary_file_header[12:12+24*2])
(ntraces, nauxtraces, deltat_us, deltat_us_orig, nsamples,
nsamples_orig, format, ensemble_fold) = hvals[0:8]
(segy_revision, fixed_length_traces, nextended_headers) = \
struct.unpack(endianness+'3H', binary_file_header[100:100+3*2])
if ntraces == 0 and nauxtraces == 0:
ntraces = 1
formats = {
1: (unpack_ibm_f4, 4, "4-byte IBM floating-point"),
2: (endianness+'i4', 4, "4-byte, two's complement integer"),
3: (endianness+'i4', 2, "2-byte, two's complement integer"),
4: (None, 4, "4-byte fixed-point with gain (obolete)"),
5: (endianness+'f4', 4, "4-byte IEEE floating-point"),
6: (None, 0, "not currently used"),
7: (None, 0, "not currently used"),
8: ('i1', 1, "1-byte, two's complement integer")}
dtype = formats[format][0]
sample_size = formats[format][1]
if dtype is None:
raise SEGYError('unsupported sample data format %i: %s' % (
format, formats[format][2]))
for ihead in range(nextended_headers):
f.read(nbthx)
atend = False
while not atend:
for itrace in range((ntraces+nauxtraces)):
trace_header = f.read(nbtrh)
if len(trace_header) == 0:
atend = True
break
if len(trace_header) != nbtrh:
raise SEGYError('incomplete trace header')
(scoordx, scoordy, gcoordx, gcoordy) = \
struct.unpack(endianness+'4f', trace_header[72:72+4*4])
(ensemblex, ensembley) = \
struct.unpack(endianness+'2f', trace_header[180:180+2*4])
(ensemble_num,) = \
struct.unpack(endianness+'1I', trace_header[20:24])
(trensemble_num,) = \
struct.unpack(endianness+'1I', trace_header[24:28])
(trace_number,) = \
struct.unpack(endianness+'1I', trace_header[0:4])
(trace_numbersegy,) = \
struct.unpack(endianness+'1I', trace_header[4:8])
(orfield_num,) = \
struct.unpack(endianness+'1I', trace_header[8:12])
(ortrace_num,) = \
struct.unpack(endianness+'1I', trace_header[12:16])
# don't know if this is standard: distance to shot [m] as int
(idist,) = struct.unpack(endianness+'1I', trace_header[36:40])
tvals = struct.unpack(
endianness+'12H', trace_header[94:94+12*2])
(nsamples_this, deltat_us_this) = tvals[-2:]
tscalar = struct.unpack(
endianness+'1H', trace_header[214:216])[0]
if tscalar == 0:
tscalar = 1.
elif tscalar < 0:
tscalar = 1.0 / tscalar
else:
tscalar = float(tscalar)
tvals = [x * tscalar for x in tvals[:-2]]
(year, doy, hour, minute, second) = \
struct.unpack(endianness+'5H', trace_header[156:156+2*5])
# maybe not standard?
(msecs, usecs) = struct.unpack(
endianness+'2H', trace_header[168:168+4])
try:
if year < 100:
year += 2000
tmin = calendar.timegm(
(year, 1, doy, hour, minute, second)) \
+ msecs * 1.0e-3 + usecs * 1.0e-6
except Exception:
raise SEGYError('invalid start date/time')
if fixed_length_traces:
if (nsamples_this, deltat_us_this) \
!= (nsamples, deltat_us):
raise SEGYError(
'trace of incorrect length or sampling '
'rate (trace=%i)' % itrace+1)
if load_data:
datablock = f.read(nsamples_this*sample_size)
if len(datablock) != nsamples_this*sample_size:
raise SEGYError('incomplete trace data')
if isinstance(dtype, str):
data = num.fromstring(datablock, dtype=dtype)
else:
data = dtype(datablock)
tmax = None
else:
f.seek(nsamples_this*sample_size, 1)
tmax = tmin + deltat_us_this/1000000.*(nsamples_this-1)
data = None
if data is not None and isinstance(dtype, str) and (
str(dtype).startswith('<')
or str(dtype).startswith('>')):
data = data.astype(str(dtype)[1:])
tr = trace.Trace(
'',
'%05i' % (line_number),
'%02i' % (ensemble_num),
'%03i' % (ortrace_num),
tmin=tmin,
tmax=tmax,
deltat=deltat_us_this/1000000.,
ydata=data,
meta=dict(
orfield_num=orfield_num,
distance=float(idist)))
yield tr
except (OSError, SEGYError) as e:
raise FileLoadError(e)
finally:
f.close()
