Commercial seismic software can be sources of non-standard SEGY formats. In addition to non-standard usage of the official header fields, commercial variations on SEGY may employ definitions of parts of the optional SEGY header fields.
A remedy for this problem, supplied by Matthias Imhoff of Virginia Tech, is a remapping feature in segyread, which allows nonstandard fields to be remapped into compatible locations in the SU header. The options remap= allows the destination SU header fields to be specified, while byte= specifies the byte location in the SEGY trace header, and its data type.
For the example of Landmark BCM2D format, header fields 73 and 77 are floats, but these are int's in the standard SEGY format and are hence also int's in the SU format. BCM2D also has to header fields set as longs at bytes 181 and 185. The following usage of segyread
% segyread tape=... remap=d1,d2,gelev,selev byte=73f,77f,181l,185l > ...
The floats at 73 and 77 are mapped to d1 and d2, while the long integers at 181 and 185 are mapped to gelev and selev, which are integers in the SU format. By selecting compatible destination fields, no precision is lost.