Hi Dave-
Dave Dempsey wrote:
I wanted to plot a vertical cross section of streamlines, but that
capability doesn't seem to be present in the IDV v2.0, unless I'm
missing something. Could this be another programming project for IDV
users comfortable with Jython? (I'm not there yet.)
The underlying VisAD system does not support 3D streamlines
(i.e. a cross section) at this time. Perhaps one of the
streamline experts could comment on this.
As an alternative, I figured out how to use the existing system formula
"Make flow vectors from u, v, and w data" to plot a vertical cross
section of flow vectors. The formula requires u, v, and w fields as
input. However, the NAM and GFS model output files contain pressure
vertical velocity (omega) fields rather than w fields. Does this mean
that the formula will get the sign of the vertical component reversed?
(It certainly doesn't seem capable of converting omega fields to w
fields, given that that would seem to require the geopotential height
field at multiple times and the temperature field, but if it got the
sign right then there'd still be useful qualitative info in the vector
computed from omega and horizontal velocity.)
I'm not an object-oriented programmer so I got lost trying to trace the
code that renders the 3-D flow vectors to see how it treats the sign of
the vertical velocity. The formula invokes the
ucar.unidata.data.grid.DerivedGridFactory class, which invokes the
createFlowVectors method, which invokes the visad class FieldImpl, which
invokes ....
Can anyone comment on what the "Make flow vectors from u, v, and w data"
formula does with u, v, and omega fields?
The formula expects that the 3 fields (u,v,w) are in units of m/s
(or something compatible) and as you note, the models have
omega, not w. Apparently, the IDV does plot omega for
w, but the display will only be qualitative as you note. If you want
to reverse the sign, then when you select the "w" parameter, instead of
selecting omega, select the formula System->Negate a field
which will then prompt you for what you want to negate. At
that point, select your omega field.
No programming necessary. ;-)
Don
*************************************************************
Don Murray UCAR Unidata Program
dmurray@xxxxxxxxxxxxxxxx P.O. Box 3000
(303) 497-8628 Boulder, CO 80307
http://www.unidata.ucar.edu/staff/donm
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