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[IDV #DFN-921227]: Obs Wind direction & speed to Streamline

Greetings Eric,

> Hi
> Currently, I have obs wind direction (in degree) and speed (m/sec) data and
> which can be used to draw wind barb in IDV.
> Question 1:
> I want to use same set of data to draw the streamlines.  I tried to put
> the direction and speed into Formulas > Grids > Make flow vectors from
> u and v data.  But it cannot produce any streamlines.  Should I convert
> the direction and speed into u and v by myself or any simple way to do it?

If the IDV understands you variables to be speed / dir, then the option to make 
flow vectors from speed / dir should automatically show up under 'derived 
quantities' in the field selector (you should not need to explicitly use a 
formula). Since the IDV isn't recognizing your speed / dir variables, you need 
to add their names to the aliases for SPEED and DIR. From the top toolbar in 
the IDV, click "Tools" -> "Parameter Alias Editor." When the editor pops up, 
click the tab for "System aliases" and find SPEED and DIR under the column 
"Name". If you double click either of those, a box will pop up that will allow 
you to add your variable name to the alias list. Do that for both SPEED and DIR 
and see if that works. Once you add them, they will show up on the "User 
aliases" tab. If you ever need to add more aliases for SPEED or DIR, just go 
through the steps above, but use the entries listed under the "Users aliases" 
tab, not "System aliases."

> Question 2:
> And I noticed that the streamlines output from IDV is quite different
> from NCL..  The spacing between two streamlines in NCL are more even
> which make NCL streamlines look more evenly distributed.  Can I get a
> more evenly distributed streamlines from IDV?

Streamlines can be tricky. However, if you have streamlines plotted you can go 
to the Dashboard and under the "Displays" tab (with your streamline field 
selected), you can manipulate the behavior of the streamlines. In particular, 
you may want to play with the Streamline density, skipping a certain number of 
point in the X and Y grid space, or using a smoothing function.



> Thanks a lot. Look forwards to your reply.
> --
> Best Regards,
> Eric Fong

Ticket Details
Ticket ID: DFN-921227
Department: Support IDV
Priority: Normal
Status: Closed

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