Editing Guide to RSF file format (section)

===Reading and writing SEG-Y and SU files===
The SEG-Y format is based on the proposal of Barry et al. (1975<ref>[http://www.seg.org/SEGportalWEBproject/prod/SEG-Publications/Pub-Technical-Standards/Documents/seg_y_rev0.pdf Barry, K. M., D. A. Cavers, and C. W. Kneale,  1975, Report on recommended standards for digital tape formats: Geophysics, '''40''', 344--352]</ref>).
It was revised in 2002<ref>See http://www.seg.org/SEGportalWEBproject/prod/SEG-Publications/Pub-Technical-Standards/Documents/seg_y_rev1.pdf</ref>. The
SU format is a modification of SEG-Y used in Seismic Unix
(Stockwell, 1997<ref>Stockwell, J. W.,  1997, Free software in education: A case study of  CWP/SU: Seismic Unix: The Leading Edge, '''16''', 1045--1049.</ref>).
To convert files from SEG-Y or SU format to RSF, use the <tt>sfsegyread</tt>
program. Let us first manufacture an example file using SU utilities
(Stockwell, 1999<ref>-------- 1999, The CWP/SU: Seismic Un*x package: Computers and  Geosciences, '''25''', 415--419.</ref>):
<pre>
bash$ suplane > plane.su
bash$ segyhdrs < plane.su | segywrite tape=plane.segy
</pre>
To convert it to RSF, use either
<pre>
bash$ sfsuread < plane.su tfile=tfile.rsf endian=0 > plane.rsf
</pre>
or
<pre>
bash$ sfsegyread < plane.segy tfile=tfile.rsf \
hfile=file.asc bfile=file.bin > plane.rsf
</pre>
The endian flag is needed if the SU file originated from a little-endian machine like a Linux PC.
Several files are generated. The standard output contains an RSF file with the
data (32 traces with 64 samples each):
<pre>
bash$ sfin plane.rsf
plane.rsf:
    in="/tmp/plane.rsf@"
    esize=4 type=float form=native
    n1=64          d1=0.004       o1=0
    n2=32          d2=?           o2=?
        2048 elements 8192 bytes
</pre>
The contents of this file are displayed in the figure.
[[Image:plane.png|frame|center|The output of suplane, converted to RSF and
displayed with <tt>sfwiggle</tt>.]]
The <tt>tfile</tt> is an RSF integer-type file with the trace headers (32
headers with 71 traces each):
<pre>
bash$ sfin tfile.rsf
tfile.rsf:
    in="/tmp/tfile.rsf@"
    esize=4 type=int form=native
    n1=71          d1=?           o1=?
    n2=32          d2=?           o2=?
        2272 elements 9088 bytes
</pre>
The contents of trace headers can be quickly examined with the 
<tt>sfheaderattr</tt> program.
The <tt>file.asc</tt> is the ASCII header file for the whole record.
<pre>
bash$ head -c 242 file.asc
C      This tape was made at the
C                                                                              
C      Center for Wave Phenomena                         
</pre>
The  <tt>file.bin</tt> is the binary header file.

To convert files back from RSF to SEG-Y or SU, use the <tt>sfsegywrite</tt>
program and reverse the input and output:
<pre>
bash$ sfsuwrite > plane.su tfile=tfile.rsf endian=0 < plane.rsf
</pre>
or
<pre>
bash$ sfsegywrite > plane.segy tfile=tfile.rsf \
hfile=file.asc bfile=file.bin < plane.rsf
</pre>

If <tt>hfile=</tt> and <tt>bfile=</tt> are not supplied to <tt>sfsegywrite</tt>, the corresponding headers will be generated on the fly. The trace header file can be generated with <tt>sfsegyheader</tt>. Here is an example:
<pre>
bash$ sfheadermath < plane.rsf output=N+1 | sfdd type=int > tracl.rsf
bash$ sfsegyheader < plane.rsf tracl=tracl.rsf > tfile.rsf
bash$ sfsegywrite  < plane.rsf tfile=tfile.rsf > plane.segy
</pre>

====Unusual trace header keys====
Sometimes, SEG-Y files deviate from the standard by creating additional
trace header keys. If, for example, you find out that the SEG-Y file
contains an additional trace header key stored in bytes 225-226, you can either remap one of the standard two-byte keys
<pre>
bash&#36; sfsegyread < file.segy tfile=tfile.rsf gut=224 > file.rsf
</pre>
or create a new key
<pre>
bash&#36; sfsegyread < file.segy tfile=tfile.rsf \
key1=mykey key1_len=2 mykey=224 > file.rsf
</pre>
Any number of additional keys can be created this way.