[idvusers] plotting true wind vectors

Is anyone aware of any bugs within IDV when trying to compute "true" wind
vectors from U10 and V10, (or in 3D using U and V)?  I have plotted some
actual observations on top of my model data and while, in some instances the
model data matches up fairly well with the observations, most of the time
the barbs are completely opposite the observed wind barbs.  I would assume
the "true" wind vectors would be plotted in meteorological coordinates (i.e.
the direction from which the wind is blowing).  I tried to find the formula
IDV uses to calculate these wind vectors, but was unsuccessful in doing so.
Any ideas?

Also, when sampling the data (using a middle click), is it sampling contours
or actual values at those points?  If I sample on my domain while having the
U10, V10, and true wind vectors (from U10 and V10) plotted, the true wind
vector value always matches the U10 component and appears to not take into
account the V10 component at all.  This may be part of my problem, but
without seeing the formula used it is hard to figure out where the problem
is.

I'd appreciate any insight, comments or solutions regarding these issues.

Thanks,

-- 
Kathleen Carroll
Institute of Atmospheric Sciences
South Dakota School of Mines & Tech.
Rapid City, SD 57701