Binary data formats have a name followed by any optional attributes. The attributes control variations within a basic format. Attributes that are recognized by specific formats are described in the usp and segy sections.
DDS automatically detects the attributes of input binary data. If they conflict with attributes explicitly defined by format, a warning is issued and the override is honored. Output data attributes take predefined defaults, unless explicitly overridden. Some of these attributes are axis specific.
Padding Dead Traces:
"dense.axis
" causes dead traces to be
padded into the correct locations for that "axis" based on the
"sort.axis
" Trace Header (See
Axis Definitions). So normally the
sort Trace Header should be set to values starting at
"base.axis
" (normally one) and incrementing
by "step.axis
" until the associated axis
reaches it's "size.axis
". However,
if "grid.axis
" is defined, then it will
expect the "sort" header to start at the first "grid" value and
increment to each successive "grid" value. If a Trace Header value
extends beyond the "grid" values then it will linearly extrapolate
based on the first two or last two "grid" values. For this purpose,
the "grid" values must be monotonically increasing or decreasing.
NOTE: When padding traces on an axis, all lower axes
(other than axis 1 which can never be padded this way) must also
be flagged with "dense.axis
". For example
if "axis= t h x y" and you want to pad dead traces onto the "x" axis
then you must use something like:
out_format= asp dense.h dense.x
The follow table lists the format attributes:
Attributes Description ----------------- ------------------------------------------- integer n sample type and precision float n ieee sample type and precision float n ieeex sample type and precision float n ibm sample type and precision complex n ieee sample type and precision complex n ibm sample type and precision hdrswap binary and trace header "Little Endian" (only for segy, segy1 and su formats) ebcdic segy card header ascii segy card header zip [n] zip compression with optional level 1-9 (default 6) (only for generic DDS formats; not segy or usp) green_prefix prec "green word"† prefix & precision green_suffix prec "green word"† suffix & precision no_green_prefix no "green word"† prefix no_green_suffix no "green word"† suffix slice.axis multiple files across the given axis sync.axis given axis is flagged as synchronized dense.axis given axis is flagged as dense (non-sparse) block set the tape to blocked
where "axis
" is
either an axis name or axis number.
Example format Definitions with explicit attributes:
comment= standard SEGY tape format format= segy comment= same thing, explicitly format= segy ebcdic float 4 ibm comment= override Samples to be ieee format= segy float 4 ieee comment= x-axis is to be padded out with dead traces format= segy dense.x comment= Same thing assuming default axis=t x y format= segy dense.2
†
"Green Words" are used at times to
indicate the number of bytes in a record for "usp" and
"segy" formats.
Many of these formats are derivatives of tape formats which have
physical record marks and writing them to disk loses the record
marks. So "Green Words" are ways of checking that the data is
synchronized correctly with the traces. Now days, usp
datasets have only a 4 byte "green word" prefix and segy
datasets typically do not use them at all.