The fga file format, used for vector fields, is fairly simple. It’s basically a .csv where the final character is a comma. Spaces are ignored. It starts with 3 integers for the field resolution. Then 3 floats each for the bounding box minimum, and the bounding box maximum. Then it’s just a list of floats where every consequent set of 3 is a vector. So the total length of the list is 9+3resolution.xresolution.y*resolution.z
For example, a 128128128 vector field, 100 world units in each dimension, and centered on zero, is 6291465 elements long and looks like:
128, 128, 128,-50.0, -50.0, -50.0, 50.0, 50.0, 50.0, 8.0331274, -1.706719, -3.706719, ...(6291450 elements skipped)...-7.686547, -25.278095, -0.673845,
So you can use whatever you want to generate a string like that. Put it in an fga file and it will import into UE4.