Common File Layout for .cgd Files

This diagram illustrates the common file layout for .cgd files, using the old BC format.

A large box on the left represents the node "ROOT", with node header values listed below.

   ipar(1) = imax
   ipar(2) = jmax
   ipar(3) = kmax
   ipar(4) = nzone
   ipar(5) = mxpts

   cpar(1) = Main title
   cpar(2) = Sub-title

Stored in the root node is the variable BLAREA, dimensioned 128.

Two boxes are attached to the root node - one representing a structured zone node and one representing an unstructured zone node. Both have the name "ZONE N", where N, the zone number, is a three-digit integer from 1 to NZONE.

The structured zone node header contains the values listed below.

   ipar(1)     = idim
   ipar(2)     = jdim
   ipar(3)     = kdim
   ipar(4)     = nfrgpt
   ipar(9)     = 0
   ipar(20-25) = Boundary type code

   fpar(1-39) = Reserved
   fpar(39-n) = Application

   cpar(1) = Zone title
   cpar(2) = Grid generator name

Shown below the structured zone node header are the variables stored in the zone node. These are x, y, z, IBLANK, ui, vi, and wi, all dimensioned (idim,jdim,kdim).

If ipar(i) = 13, where i is from 20 to 25, a node named "BNDRY n", where n is an integer from 1 to 6, is located below the structured zone node. The node header values aren't applicable. The variables stored in this node are NZN, NBD, I1, I2, F1, and F2. For n = 1 or 2, these are dimensioned (jmax,kmax); for n = 3 or 4, these are dimensioned (kmax,imax); and for n = 5 or 6, these are dimensioned (jmax,imax).

If nfrgpt > 0, a node named "FRNG BND" is also located below the structured zone node. The node header values aren't applicable. The variables stored in this node are NZN, ZHOLE, I1-I3, F1-F3, IFRG, JFRG, and KFRG, all dimensioned nfrgpt.

The unstructured zone node header contains the values listed below.

   ipar(1)  = npnts
   ipar(2)  = nedge
   ipar(3)  = nface
   ipar(4)  = ncell
   ipar(5)  = max pts/face
   ipar(6)  = max pts/cell
   ipar(7)  = nsurfs
   ipar(9)  = 1 or 2
   ipar(20) = nbdpts
   ipar(21) = nbdedge
   ipar(22) = nbdface
   ipar(23) = bctype

   fpar(1-39) = Reserved
   fpar(39-n) = Application

   cpar(1) = Zone title
   cpar(2) = Grid generator name

Shown below the unstructured zone node header are the variables stored in the zone node. These are x, y, z, all dimensioned nbdpts; facpi, where i = 1 to ipar(5); and srfid, srfbc, srfsiz, srfoff, and srfpts, all dimensioned nsurfs.

If srfbc(n) = 13, for n = 1 to nsurfs, a node named "BNDRY n" is located below the unstructured zone node. The node header contains the variable ipar(1), equal to the BC version. The variables stored in this node are NZN; NBD; and Ii and Fi, where i = 1 to ipar(5), and for ipar(9) = 1 to srfsiz(n).

If ncell > 0, a node named "INTERIOR" is also located below the unstructured zone node. The node header values aren't applicable. The variables stored in this node are x, y, and z, all dimensioned npnts-nbdpts; celpi, where i = 1 to maxpts/cell, dimensioned ncell; and celtyp.