An example of defining and using a custom Binary Reel Header definition.

Author: rob-smallshire

examples/custom_header.py

@@ -0,0 +1,120 @@
+#!/usr/bin/env python3
+
+"""Demonstrates how to customise a header format.
+
+Standard SEG-Y requires that all header fields are two's complement (i.e. signed)
+integers with a width of two or four bytes. In Segpy these are represented by the
+types Int16 and Int32 from the field_types module.  For many header fields,
+negative values would be nonsensical, so in the header specifications field values
+can be further constrained to be non-negative by the use of the NNInt16 and NNInt32
+types which require non-negative (NN) values. Note that these are not the same as
+*unsigned* two- or four-byte integers, which would have an expanded range.
+
+In this module, we show how to define and use a non-standard UInt16 type which
+can accommodate the full unsigned 16-bit range from 0 to 65535.
+
+Usage:
+
+    custom_header.py <in.segy>
+
+"""
+
+import os
+
+import sys
+import traceback
+
+from segpy.binary_reel_header import BinaryReelHeader
+from segpy.datatypes import SegYType
+from segpy.field_types import IntFieldMeta
+from segpy.header import field
+from segpy.reader import create_reader
+
+
+# Standard SEG-Y does not support 16-bit unsigned integer values in headers.
+# This section customises SEG-Y to support them.
+
+class UInt16(int,
+            metaclass=IntFieldMeta,
+            min_value=0,       # Use the full-range for unsigned
+            max_value=65535,   # 16-bit integers
+            seg_y_type=SegYType.NNINT16):   # The underlying NNINT16 type is actually read as an unsigned type.
+    """16-bit unsigned integer."""
+    pass
+
+
+# Subclass the standard reel header to specialize one of its fields to have a type of UInt16.
+
+class CustomBinaryReelHeader(BinaryReelHeader):
+
+    num_samples = field(
+        UInt16, offset=3221, default=0, documentation=
+        """Number of samples per data trace. Mandatory for all types of data.
+        Note: The sample interval and number of samples in the Binary File Header should be for the primary set of
+        seismic data traces in the file."""
+    )
+
+
+def report_segy(in_filename):
+    with open(in_filename, 'rb') as in_file:
+
+        # Create a reader using the CustomBinaryReelHeader format.
+        segy_reader = create_reader(
+            in_file,
+            binary_reel_header_format=CustomBinaryReelHeader)
+
+        print()
+        print("Filename:             ", segy_reader.filename)
+        print("SEG Y revision:       ", segy_reader.revision)
+        print("Number of traces:     ", segy_reader.num_traces())
+        print("Data format:          ",
+              segy_reader.data_sample_format_description)
+        print("Dimensionality:       ", segy_reader.dimensionality)
+
+        try:
+            print("Number of CDPs:       ", segy_reader.num_cdps())
+        except AttributeError:
+            pass
+
+        try:
+            print("Number of inlines:    ", segy_reader.num_inlines())
+            print("Number of crosslines: ", segy_reader.num_xlines())
+        except AttributeError:
+            pass
+
+        print("=== BEGIN TEXTUAL REEL HEADER ===")
+        for line in segy_reader.textual_reel_header:
+            print(line[3:])
+        print("=== END TEXTUAL REEL HEADER ===")
+        print()
+        print("=== BEGIN EXTENDED TEXTUAL HEADER ===")
+        print(segy_reader.extended_textual_header)
+        print("=== END EXTENDED TEXTUAL_HEADER ===")
+
+
+def main(argv=None):
+    if argv is None:
+        argv = sys.argv[1:]
+
+    try:
+        in_filename = argv[0]
+    except IndexError:
+        print(globals()['__doc__'], file=sys.stderr)
+        return os.EX_USAGE
+
+    try:
+        report_segy(in_filename)
+    except (FileNotFoundError, IsADirectoryError) as e:
+        print(e, file=sys.stderr)
+        return os.EX_NOINPUT
+    except PermissionError as e:
+        print(e, file=sys.stderr)
+        return os.EX_NOPERM
+    except Exception as e:
+        traceback.print_exception(type(e), e, e.__traceback__, file=sys.stderr)
+        return os.EX_SOFTWARE
+    return os.EX_OK
+
+
+if __name__ == '__main__':
+    sys.exit(main())