On May 31, 10:21 pm, "ClauDe " <acerxen...@hotmail.com> wrote:
> > The result is wrong; it should obviously be 123.4 degrees.
>
> > Seriously, what kind of response do you expect to get?
> > You don't say anythiong about how these data have been
> > measured, what the variables represent, how you have
> > got your first result, or why you expect the result
> > you indicate.
>
> > Or defined what you mean by the term 'mean direction'.
>
> > Answer the questions indicated above (not so much for us
> > as for yourself), and you might eventually be getting
> > somewhere.
>
> > Rune
>
> hey Rune,
>
> ok, lets see.
> I have data of the current directions and velocities from moored Currentmeter. The data start point is Nov2009 and end is Aug2010.
> With these data I plotted a stickplot(drawn by currentvelocity and direction), that indicates/shows an average direction towards the SouthEast (by eye). I also plotted these data as a PVD (progressive vector diagram) which makes "pseudo trajectories" and it shows an SouthEast direction as well (by eye).
>
> Now, I have to plot the mooring position into a bathymetry plot and on that plot I have to draw an arrow which is constructed out of the mean direction and mean velocity(length of this arrow), so to speak the average values.
> This arrow shall indicate what the mean flow is and where it's going.
>
> Ok, I could draw it by eye but I have to use the average values. Average of direction makes a little problem.
>
> What I hoped to get here is an equation or sth. for MATLAB to calculate the average direction out of a Vector with directions that were measured on a mooring.
>
> I tried:
> rad = 2*pi/360
> dirvecmean=atan2(umean,vmean);
> dirmean1=dirvecmean / rad;
>
> But this gives me an Northwest direction which is not what I saw on my plots... that's why I'm confused!
>
> Did that help at all? Or did I confused you even more with that? ;)
> Anyway, thanks for your help!
Twice you've referred to sth:
"I expect sth like 300° ...."
"What I hoped to get here is an equation or sth. ....."
I analyse ADP/ADCP current records just about every week, but I've
never heard of a "sth"
What is it?
Getting average direction is simply:
angle(mean(v+i*u))*pi/180 degrees from North
But you may need to correct for magnetic N, which is what most current
meters measure.
Where I live, the correction to get True North is 23.4 deg, which is
quite significant.
Note: you cannot simply average the direction, you must average the
complex current vector, then convert to direction.
