The fmt Dictionary may also contain "sort:" Definitions which determine the Trace Header words used as the sort word for the various axes (the first axis does not have a sort header). In general the sort fields are defined by:

sort:a=field
sort:old_fmt.n:new_fmt=field
    

• a is the axis name or number
• old_fmt is the old format name or *
• n is axis number, old sort header or *
• new_fmt is the new format name or *
• field is the new sort header

The header words TrcNum and RecNum for usp, for example, can be specified as the sort field for the second and third axes by:

sort:2= TrcNum
sort:3= RecNum
    

Changing to a different format may require new header words to be specified as the sort fields. So for example anytime usp data is created from segy data, if "CdpNum" is the sort header of any axis, then that same axis will then have "TrcNum" as the sort header in the usp dataset.

sort:segy.CdpNum:usp= TrcNum
sort:segy.FieldRecNum:usp= PrRcNm