The problem is that wind could veer as well as back so it is important that your algorithm takes into account the sense (direction) of the operations.
For example, let:
. w0 be your initial wind direction
. v0 be your initial wind speed
. h0 be your initial altitude
. w1 be your final wind direction
. v1 be your final wind speed
. h1 be your final altitude
The important bit here is that it's not the same going from x0 to x1 than going from x1 to x0.
In that case, for an altitude hn your W/V is:
vn = (v1-v0) / (h1-h0) * (hn-h0) + v0
w0 = w0 % 360 [ where % denotes the modulo operation ]
w1 = w1 % 360 [ so that 0 >= w > 360 ]
w1' = (w1 <= w0 ? w1 : (w1 + 360)) [ make sure w1' <= w0 ]
wn = ((w1'-w0) / (h1-h0) * (hn-h0) + w0) % 360
I'm pretty sure Excel provides all the features needed to implement the above algorithm. I'm sorry I can't provide the specific syntax, but I don't use Excel.
Hope this helps,
LH2
Last edited by LH2; 28th November 2006 at 19:45.
Reason: Spelling + omission