Creates a 3-dimensional grid of values.
gx, gy, and gz give the origin and the step width of the grid for the x, y and z direction, e.g. gx = (x0, dx), gy = (y0, dy) and gz = (z0, dz).
gx, gy and gz are typeless nodes, to which the number nodes x0, dx, y0, dy, z0 and dz are connected, and m is a typeless node to which the layers of the 3-dimensional value matrix are connected.
The following variations of this keyword exist (some of them define the same internal structures, and are only defined to allow consistent naming conventions):