DDF (Domain Data File) Format

DDF (Domain Data File) is a data file format to define a domain. Typically, a domain is given its boundary as collection of vertices, lines, contours, holes. A DDF file is a simple text file containing the definition of any domain.
The main principle here is that any information in the file is contained in a line and is defined by a keyword following the rules :

• The first line must contain at the first columns the string #DOMAIN!
• Keyword dim starts a line that gives the space dimension. An integer number (between 1 and 3) must follow this keyword. Note this keyword is optional, its default value being 2
• Each vertex must be introduced by a line starting with the keyword vertex. This keyword must be followed by the following data :
  
  

  label	Label of vertex (integer)
  x[1]	First coordinate of vertex (real number)
  ...	... ...
  x[dim]	dim-th coordinate of vertex (real number)
  size	Mesh size around the vertex (real number)
  code	Code associated to node (integer)

  
  

• Each straight line must be introduced by a line starting with the keyword line. A line is given by two vertices that define its both ends. This keyword must be followed by the following data :
  
  

  label	Label of line (integer)
  v1	Label of first vertex (integer)
  v2	Label of second vertex (integer)
  Ncode	Code associated to line generated nodes (integer)
  Scode	Code associated to line generated sides (integer)

• Each circular arc must be introduced by a line starting with the keyword circle. A circular arc is given by two vertices that define its both ends. This keyword must be followed by the following data :
  
  

  label	Label of line (integer)
  v1	Label of first vertex (integer)
  v2	Label of second vertex (integer)
  cx	x-coordinate of center of circle (real)
  cy	y-coordinate of center of circle (real)
  r	Radius of circle (real)
  orientation	Orientation of arc (1: Direct, -1: Inverse (integer)
  Ncode	Code associated to line generated nodes (integer)
  Scode	Code associated to line generated sides (integer)
  nb	Number of sub-intervals (integer)

• Each contour must be defined by a line starting with the keyword contour. A contour is a closed union of lines (or arcs). The term contour is concerned with external boundaries. Internal ones are called holes. The syntax of a line beginning with keyword contour is the following :
  
  

  label	Label of contour (integer)
  nb	Number of lines (integer)
  c[1]	Label of the fist line in contour (integer)
  ...	...
  c[nb]	Label of the nbth line in contour (integer)

• Each hole must be defined by a line starting with the keyword hole. A hole is a closed union of lines (or arcs). The syntax of a line beginning with keyword hole is the following :
  
  

  label	Label of hole (integer)
  nb	Number of lines (integer)
  h[1]	Label of the first line in hole (integer)
  ...	...
  h[nb]	Label of the nbth line in hole (integer)

• Each subdomain must be defined by a line starting with the keyword subdomain. A subdomain is defined by a contour or a collection of contours. The syntax of a line beginning with keyword subdomain is the following :
  
  

  label	Label of contour defining the subdomain (integer)
  ref	Reference number for subdomain (integer)

• The number of degrees of freedom per node must be defined by a line starting with the keyword dof. Note that this number is assigned the value 1 by default
  The syntax of a line beginning with keyword dof is the following :
  

  n	Number of degrees of freedom per node (integer)

• A rectangle can be defined in one line starting by keyword Rectangle. This choice corresponds to the definition of a rectangular domain, not a union of a rectangle and other sub-domains. The resulted mesh is stored in a file after reading this line. The rectangle is given by [0,lx]*[0,ly] The syntax of a line beginning with keyword Rectangle is the following :
  
  

  lx	Length of rectangle (real number)
  ly	Height of rectangle (real number)
  nex	Number of sub-intervals in the x-direction (integer)
  ney	Number of sub-intervals in the y-direction (integer)
  ratio	Progression ratio. A value of 1 corresponds to a uniform mesh (real number)
  bs	Store (1) or not (0) all boundary sides (integer)
  c1	Code of nodes on the line y=0 (integer)
  c2	Code of nodes on the line x=lx (integer)
  c3	Code of nodes on the line y=ly (integer)
  c4	Code of nodes on the line x=0 (integer)
  mesh_file	Name of mesh file where to store the resulted mesh (string)

• A disk can be defined in one line starting by keyword Disk. This choice corresponds to the definition of a disk, not a union of a disk and other sub-domains. The resulted mesh is stored in a file after reading this line. The syntax of a line beginning with keyword Disk is the following :
  
  

  R	Radius of disk (real number)
  cx	x-coordinate of center of disk (real number)
  cy	y-coordinate of center of disk (real number)
  type	Mesh type (0≤type≤2). Corresponds to various types of triangulations (integer)
  ns	Number of subdivisions of the circumference (integer)
  nl	Number of layers (subdivisions of the radius) (integer)
  bs	Store (1) or not (0) boundary sides (integer)
  nb_dof	Number of degrees of freedom per node (integer)
  dc	Code of nodes on the boundary (integer)
  nc	Code of sides on the boundary (integer)
  mesh_file	Name of mesh file where to store the resulted mesh (string)

• Mesh generation is made by a line starting with the keyword mesh. The syntax of a line beginning with keyword mesh is the following :
  

  mesh_file

  Name of file where the resulting mesh is to be stored (string)

• The last line of the DDF file must contain the keyword EOF (as End Of File).