xenial (5) dirfile.5.gz

NAME

       dirfile — a filesystem-based database format for time-ordered binary data

DESCRIPTION

       The  dirfile  database format is designed to provide a fast, simple format for storing and reading binary
       time-ordered data.  Dirfiles can be read using the GetData library.

       The dirfile database is centred around one or more time-ordered data streams (a time stream).  Each  time
       stream  is  written  to  disk  in a separate file, in its native binary format.  The name of these binary
       files correspond to the time stream's field name.  Two time streams may have different constant  sampling
       frequencies  and  mechanisms exist within the dirfile format to ensure these time streams remain properly
       sequenced in time.

       To do this, the time streams in the dirfile are subdivided into frames.  Each frame contains  an  integer
       number of samples of each time stream.  When synchronous retrieval of data from more than one time stream
       is required, position in the dirfile can be specified in frames, which will ensure synchronicity.

       The binary files are all located in a central directory, known as the dirfile directory.  The dirfile  as
       a whole may be referred to by its dirfile directory path.

       Included  in  the  dirfile  along  with the time streams is the dirfile format specification, which is an
       ASCII text file called format located in the dirfile directory.  This file fully specifies the  dirfile's
       metadata.  For the syntax of this file, see dirfile-format(5).

       Version  3  of  the  Dirfile  Standards introduced the large dirfile extension.  This extension added the
       ability to distribute the dirfile metadata among multiple files (called fragments)  in  addition  to  the
       format  file, as well as the ability to house portions of the database in subdirfiles.  These subdirfiles
       may be fully fledged dirfiles in their own right, but may also  be  contained  within  a  larger,  parent
       dirfile.  See dirfile-format(5) for information on specifying these subdirfiles.

       In  addition  to the raw fields on disk, the dirfile format specification may also specify derived fields
       which are calculated from one or more raw or derived time streams.  Derived fields behave identically  to
       raw  fields  when  read  via  GetData.  See dirfile-format(5) for a complete list of derived field types.
       Dirfiles may also contain both numerical and  character  string  constant  scalar  fields,  also  further
       outlined in dirfile-format(5).

       Dirfiles  are  designed to be written to and read simultaneously. The dirfile specification dictates that
       one particular raw field (specified either explicitly or implicitly by the format specification) is to be
       used  as  the reference field: all other vector fields are assumed to have at least as many frames as the
       reference field has, and the size (in frames) of the reference field is used as the size of  the  dirfile
       as a whole.

       Version  6  of the Dirfile Standards added the ability to encode the binary files on disk.  Each fragment
       may  have  its  own  encoding  scheme.  Notably  this  can  be  used  to  compress  these   files.    See
       dirfile-encoding(5) for information on encoding schemes.

   Complex Number Storage Format
       Version  7  of  the Dirfile Standards added support for complex valued data.  Two types of complex valued
       data are supported by the Dirfile Standards:

       •   A 64-bit complex number consisting of a IEEE-754 standard 32-bit single precision floating point real
           part and a IEEE-754 standard 32-bit single precision floating point imaginary part, and

       •   A  128-bit  complex  number  consisting of a IEEE-754 standard 64-bit double precision floating point
           real part and a IEEE-754 standard 64-bit double precision floating point imaginary part.

       No integer-type complex numbers are supported.

       Unencoded complex numbers are stored on disk in "Fortran order", that is  with  the  IEEE-754  real  part
       followed  by the IEEE-754 imaginary part.  The specified endianness of the two components follows that of
       purely real floating point numbers.  Endianness does not affect the ordering of the  real  and  imaginary
       parts.  This format also conforms to the C99 and C++11 standards.

       To  aid  in  using  complex  valued  data,  dirfile field codes may contain a representation suffix which
       specifies a function to apply to the  complex  valued  data  to  map  it  into  purely  real  data.   See
       dirfile-format(5).

AUTHORS

       The  Dirfile  format  was  developed  by  C.  B.  Netterfield <netterfield@astro.utoronto.ca>.  It is now
       maintained by D. V. Wiebe <getdata@ketiltrout.net>.

SEE ALSO

       dirfile-encoding(5), dirfile-format(5)