PLOT3D is an old structured grid format commonly used for Curvilinear Grids.
PLOT3D is a multifile format typically consisting of the following files:
- .xyz File - This contains the grid information, XYZ values for every IJK location
- .q File - Commonly referred to as the "Solution" file, this contains the simulation results
- Function File - This is an optional data file containing data typically not found in the solution file
Solution File Format
The solution file typically contains the following three fields:
- Flow Density - Scalar
- Flow Momentum - Vector
- Flow Energy - Scalar
The values are not interlaced, so first all the Density values are in the file, then all the Momentum X values, then all the Momentum Y values, etc. This makes skipping undesired fields relatively easy and fast during load.
When stored in binary, all values are in 4-byte floating-point format. When written in FORTRAN, record markers exist at the beginning and end of each field.
PLOT3D does support MultiBlock Grids. Each block is a structured grid. The number of blocks is the first number in the file, with the following lines denoting the IJK sizes. Then the grid locations or data are written for each block separately and concatenated into the file.
Optional Function File
The optional function file follows a nearly identical format to the solution file. The only difference is that there is no restriction on what type of data is written; any number of scalars may be written to the file. When using MultiBlock data with the optional function file, the IJK specification lines contain a fourth number indicating the number of scalars per point.
There is a variation on the PLOT3D format known as "Unstructured PLOT3D" that can contain unstructured grid information.
There is also a variation that uses 8-byte double-precision floating point in binary versions.