Stretched grids are those whose grid cell spacing is non-unform along one or more axis, and futhermore can be expressed as a function of a single variable. An example of a stretched grid in the Cartesian coordinate system is the Rectilinear grid. To generate a VDC for a stretched grid, the .vdf file associated with the VDC must specify that the grid type is "stretched", and the coordinate spacing for each non-uniformly spaced axes must be specified. The grid type can be specified by the "-gridtype" option found on many of the vdf creation command line utilities. Similarly, the coordinates of a stretched dimension may be specified by the "-xcoords", "-ycoords", and/or "-zcoords" command line option, as appropriate. The "-xcoords", "-ycoords", and "-zcoords" options expect a file path as an argument that contains an ASCII description of the coordinates. The coordinates must be mononically increasing, and the number of coordinates must match the dimension of the stretched axes. For example, if the file named "zcoords.txt" contained the contents:
0.0
0.1
0.25
0.5
1.0
then the following command might be used to generate a .vdf file for a grid with a stretched Z axes:
vdfcreate -dim 128x128x5 -zcoords zcoords.txt -gridtype stretched myfile.vdf
