Read Poststack data

Meta Information

Use cigsegy.metaInfo to scan the SEG-Y file and obtain some meta information of the file, such as shape, dt, data format …

From textual header, we may get some key information, such as inline/crossline location, inline/crossline step, cdp x/y location, … See Textual Header.

# inline/xline/istep/xstep/xloc/yloc = 189/193/2/1/73/77
>>> cigsegy.metaInfo('rogan.sgy', iline=189, xline=193, istep=2, xstep=1, xloc=73, yloc=77)
# shape: (n-inline, n-crossline, n-time) = (663, 769, 1001)
# N traces: 380762
# interval: di(iline) = 35.00 ft, dx(xline) = 17.50 ft, dt = 4 ms
# range: inline: 360 - 1684, crossline: 1764 - 2532, t: 0 - 4000.0 ms
# trace sorting code: Unknown
# scalar: 1, data format: 4-byte IBM floating-point
# (key info) iline: 189, xline: 193, xloc:  73, yloc:  77
#         istep:   2, xstep:   1

>>> cigsegy.metaInfo('rogan.sgy')
# shape: (n-inline, n-crossline, n-time) = (663, 769, 1001)
# N traces: 380762
# interval: di(iline) = 35.00 ft, dx(xline) = 17.50 ft, dt = 4 ms
# range: inline: 360 - 1684, crossline: 1764 - 2532, t: 0 - 4000.0 ms
# trace sorting code: Unknown
# scalar: 1, data format: 4-byte IBM floating-point
# (key info) iline: 189, xline: 193, xloc:  73, yloc:  77
#         istep:   2, xstep:   1

In some SEG-Y files, we cannot get useful information from textual header, i.e., don’t know iline/xline/istep/xstep. You can just ignore them, and cigsegy will automatically guess the locations and steps of inline and crossline.

Note

For the previous version, you may need to set use_guess=True. For the lasted version, you don’t need do this, just ignore them.

>>> cigsegy.metaInfo('rogan.sgy', 189, 193) # ignore istep and xstep
# shape: (n-inline, n-crossline, n-time) = (663, 769, 1001)
# N traces: 380762
# interval: di(iline) = 35.00 ft, dx(xline) = 17.50 ft, dt = 4 ms
# range: inline: 360 - 1684, crossline: 1764 - 2532, t: 0 - 4000.0 ms
# trace sorting code: Unknown
# scalar: 1, data format: 4-byte IBM floating-point
# (key info) iline: 189, xline: 193, xloc:  73, yloc:  77
#         istep:   2, xstep:   1

To get the meta information in dict format, use cigsegy.tools.get_metaInfo:

>>> meta = cigsegy.tools.get_metaInfo('rogan.sgy')
>>> print(meta)
# {'iline': 189, 'istep': 2, 'offset': 37, 'ostep': 1, 'xline': 193,
# 'xloc': 73, 'xstep': 1, 'yloc': 77, 'dformat': 1, 'di': 34.99929428100586,
# 'dt': 4000, 'dx': 17.499540328979492, 'end_iline': 1684, 'end_offset': 0,
# 'end_xline': 2532, 'esize': 4, 'fillNoValue': 0.0, 'ndim': 3, 'ni': 663,
# 'no': 1, 'nt': 1001, 'ntrace': 380762, 'nx': 769, 'scalar': 1,
# 'start_iline': 360, 'start_offset': 0, 'start_time': 0, 'start_xline': 1764,
# 'trace_sorting_code': 0, 'tracesize': 4244, 'unit': 'ft'}

Note

You can use cigsegy.tools.trace_count('rogan.sgy') to get the trace number.

Read 3D poststack data

Use cigsegy.fromfile to read data as numpy.ndarray:

>>> d = cigsegy.fromfile('rogan.sgy', iline=9, xline=21, istep=2, xstep=1)
>>> d.shape
# (663, 769, 1001) # (n-inline, n-crossline, n-time)

Use cigsegy.tofile to convert SEG-Y file to a binary file (without any headers). When using cigsegy.tofile(), you don’t have to worry about running out of memory. Therefore, this function is very useful when dealing with huge files.

>>> cigsegy.tofile('rogan.sgy', 'out.dat', iline=9, xline=21, istep=2, xstep=1)

Read unsorted 3D poststack data

If the SEG-Y file is unsorted, you can use cigsegy.tools.full_scan to scan the geometry of the file, and then use cigsegy.tools.load_by_geom to read the data.

But, please note that cigsegy.tools.full_scan is slow, because it needs to scan the whole file. Besides, iline and xline are required to be specified.

>>> geom = cigsegy.tools.full_scan('rogan.sgy', 189, 193) # must pass iline and xline
>>> d = cigsegy.tools.load_by_geom('rogan.sgy', geom)

Read 3D poststack data by ignoring header

You can use cigsegy.collect('rogan.sgy').reshape(ni, nx, nt) to do it.

Use plot tools you will see like:

rogan3d

Read 2D poststack data

Use cigsegy.collect to read all traces as a 2D array:

>>> d = cigsegy.collect('L03_MIG_CB.sgy')
>>> d.shape
# (5038, 6000) # (n-traces, n-time)

Note

collect function can read traces from beg to end.

  • default, collect all traces

>>> d = cigsegy.collect('L03_MIG_CB.sgy')
>>> d.shape
# (5038, 6000) # (n-traces, n-time)

  • set beg and end (0 <= beg < end <= trace_count) to collect traces from beg to end, end is not included.

>>> d = cigsegy.collect('L03_MIG_CB.sgy', 10, 100)
>>> d.shape
# (90, 6000)

  • read one trace with a trace index, this is equivalent to setting beg=index and end=0.

>>> d = cigsegy.collect('L03_MIG_CB.sgy', 100)
>>> d.shape
# (1, 6000), the 100-th trace

# equivalent to
>>> d = cigsegy.collect('L03_MIG_CB.sgy', beg=100, end=0)

  • set end=-1 to collect traces from beg to trace_count.

>>> d = cigsegy.collect('L03_MIG_CB.sgy', 1000, -1)
>>> d.shape
# (4038, 6000), range like [1000:trace_count]

Arbitrary slicing and extration

Use cigsegy.SegyNP class is a more efficient way, which treats the SEG-Y file as a 3D/2D numpy array. Please see SegyNP for more details. (From version 1.1.7)

Plot the slices, you will see:

slices

Cut a sub SEG-Y

Use cigsegy.SegyNP class is a more efficient way, which treats the SEG-Y file as a 3D/2D numpy array.

Plot region map

Use cigsegy.plot.plot_region to plot the region where the segy file was located (x/y axis is inline/crossline).

# loc: [iline, xline, istep, xstep]
>>> cigsegy.plot.plot_region('rogan.sgy', iline=9, xline=21, xxx)

You will see:

rogan

rogan.sgy file is a irregular SEG-Y file which missing some traces.

If you want to plot the region in CDP X and CDP Y axis, set mode='cdpxy', and set xloc=cdpx, yloc=cdpy if nessesary.

# loc: [iline, xline, istep, xstep]
>>> cigsegy.plot.plot_region('rogan.sgy', mode='cdpxy', iline=9, xline=21, xloc=73, yloc=77, xxx)
roganxy