My assumption is that you would have to write a piece of code that calculated the nulls position for a given range of frames, in the same fashion as you are doing for one frame, i.e calculating the outcome at each frame with a loop, and average them out.
Simplified, if your code for a given null was (A+B+C)/3
Your averaged value would be ((A1+B1+C1)/3 + (A2+B2+C2)/3 + (A3+B3+C3)/3)/3
Where A1 is a value 1 frame back, A2 a value at current frame and A3 the value at the next frame.
With a loop, you can make the range as large as you want.
The point being, you would do the full position calculation using valueAtTime() to retrieve the values of A, B and C at a given time for each of the frames in the loop and then averaged them out. Rather than retrieving the result of the NULL position calculation through valueAtTime().
Would seem less error-prone.
Kalleheikki Kannisto
Senior Graphic Designer