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NOTICE: This version of the NSF Unidata web site (archive.unidata.ucar.edu) is no longer being updated.
Current content can be found at unidata.ucar.edu.
To learn about what's going on, see About the Archive Site.
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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