Extraction of Co-ordinate Values from CFD Simulation Space

I have the numerical output from a CFD simulation which consists of ~1.5 million cells. At each node, there is a 3D co-ordinate value and corresponding fluid velocities at that location. I'm flying a quadrotor dynamic model through this environment and I need to be able to extract the correct velocity values that correspond with the location of the aircraft.

For example, in 2D space, if my quadrotor was located at (0.5,0.5), where there is no output CFD data, I'd want to be able to determine the velocity values at that location using bilinear interpolation. This means that I would need code that could obtain the nodes surrounding the quadrotor, which are (0,0), (0,1), (1,0) and (1,1) in this case. How can I achieve this in 3D space?

Apologies if the question is a tad confusing, I didn't want to make it overly long.