Editing Guide to RSF file format (section)

===Compatibility with SEPlib===
RSF is mostly compatible with its predecessor, the SEPlib file format.
However, there are several significant differences:
  
#SEPlib programs typically use the element size (<tt>esize=</tt> parameter) to distinguish between different data types: <tt>esize=4</tt> corresponds to floating point data, while <tt>esize=8</tt> corresponds to complex data. The RSF type handling mechanism is different: data types are determined from the value of the <tt>data_format</tt> parameter. Madagascar computational programs typically output files with <tt>data_format="native_float"</tt> or <tt>native_complex</tt>.
#The default data form in SEPlib programs is typically XDR and not native as it is in RSF. Thus, to make a dataset created with SEPlib readable by Madagascar programs, you would typically need to add to the history file <tt>data_format="xdr_float"</tt> or <tt>data_format="xdr_complex"</tt> . <ref group="note">For SEPlib 6.5.3 and older: Note that xdr_complex is not a valid SEPlib value, so for datasets of complex numbers encoded as pairs of floats, a dataset cannot be at the same time valid in both SEPlib and Madagascar. A valid SEPlib dataset will have esize=8 and data_format="xdr_float", but sfin will show it as having "200% of expected" data. Adding data_format="xdr_complex" to such a dataset will make sfin work as expected, but SEPlib's In or In3d will give a segmentation fault because of an unknown data type. To patch SEPlib to accept <tt>native_complex</tt> and <tt>xdr_complex</tt> data, the following changes must be made:
* In <tt>$SEPSRC/seplib_base/lib/corelibs/sep/strformats.c</tt>:
** Add "xdr_complex" and "native_complex" to the str_fmt_names structure
** Set FMT_LENGTH to 15
* In <tt>$SEPSRC/seplib_base/lib/corelibs/include/strformats.h</tt>:
** Add preprocessor directives to define FMT_XDR_COMPLEX as 8 and FMT_NATIVE_COMPLEX as 9
** Set NUM_FMT to 10
</ref>
#It is possible to pipe the output of Madagascar programs to SEPlib: <pre>bash$ sfspike n1=1 | Attr want=min</pre> (output should be: <tt>minimum value = 1 at 1</tt>). However, piping the output of SEPlib programs to RSF (or, for that matter, any other non-SEPlib programs) will result in an unterminated process. For example, the command <pre> bash$ Spike n1=1 | sfattr want=min </pre> will hang. This is because SEPlib uses sockets for piping and expects a socket connection from the receiving program, while Madagascar passes data through regular Unix pipes. 
#SEP3D is an extension of SEPlib for operating with irregularly sampled data (Biondi et al., 1996<ref>Biondi, B., R. Clapp, and S. Crawley,  1996, SEPlib90: SEPlib for 3-D  prestack data, ''in'' SEP-92,  343--364. Stanford Exploration Project.</ref>). There is no equivalent of it in RSF for the reasons explained at the beginning of this guide. Operations with irregular datasets are supported using auxiliary input files representing the geometry information.

;Notes
<references group="note" />