The math for interpolating a vector on an arbitrary location inside a vector field.

VectorFieldInterpolation.cs

public Vector3 VectorAt(float x, float y, float z) {
	if (x < 0f) x = Mathf.Abs(x);
	if (y < 0f) y = Mathf.Abs(y);
	if (z < 0f) z = Mathf.Abs(z);

	int floorX = Mathf.FloorToInt(x);
	float tx = x - floorX;
	floorX %= Dimension;
	int ceilX = Mathf.CeilToInt(x) % Dimension;

	int floorY = Mathf.FloorToInt(y);
	float ty = y - floorY;
	floorY %= Dimension;
	int ceilY = Mathf.CeilToInt(y) % Dimension;

	int floorZ = Mathf.FloorToInt(z);
	float tz = z - floorZ;
	floorZ %= Dimension;
	int ceilZ = Mathf.CeilToInt(z) % Dimension;

	// gradient is a 3D array of Vector3s
	return (tx * ty * tz * gradient[ceilX, ceilY, ceilZ] +
		tx * ty * (1 - tz) * gradient[ceilX, ceilY, floorZ] +
		tx * (1 - ty) * tz * gradient[ceilX, floorY, ceilZ] +
		tx * (1 - ty) * (1 - tz) * gradient[ceilX, floorY, floorZ] +
		(1 - tx) * ty * tz * gradient[floorX, ceilY, ceilZ] +
		(1 - tx) * ty * (1 - tz) * gradient[floorX, ceilY, floorZ] +
		(1 - tx) * (1 - ty) * tz * gradient[floorX, floorY, ceilZ] +
		(1 - tx) * (1 - ty) * (1 - tz) * gradient[floorX, floorY, floorZ]).normalized;
}