The Brookhaven Protein Data Bank stores atomic coordinate information
for protein structures in a column based format. This is designed to
be read easily read by FORTRAN programs. Indeed, if you get the
format description (from anonymous ftp to ftp.pdb.bnl.gov, the file
/pub/format.desc.ps) they show the single input line needed to read
each record type.
However, I am a C/C++ programmer in the Unix environment. It is a
easier for me to deal with field based input than column based ones.
If the fields are white space delimited I can easily use awk and perl
to manipulate the coordinate information. So I needed some way to
convert the ATOM and HETATM records of PDB files from the standard
column based format to a field based one and back again. It needed
to denote missing fields if they exist.
That converter is `pdbcat'.