[IDV #MUS-211252]: IDV v3.0b1: Streamlines colored by wind speed; winds on isosurfaces

> 
> On Sep 6, 2011, at 3:43 PM, Unidata IDV Support wrote:
> 
> >> (2) Is it possible to plot wind barbs or wind vectors on an isosurface of 
> >> another quantity other than pressure, such as potential temperature (an 
> >> isentropic surface)? To do so seems as if it would require knowing the 
> >> height field of the isosurface, which defines the topography on which the 
> >> winds would be plotted. The IDV currently can plot wind vectors on 
> >> isobaric surfaces because the geopotential heights of such surfaces are 
> >> available in forecast model data files, but if the IDV calculates the 
> >> height field for other kinds of isosurfaces as a necessary step toward 
> >> creating an isosurface plot, then couldn't winds be plotted on that 
> >> topography, too?
> 
> If I understand the second question correctly, I believe that drawing the 
> wind vectors over an isofurface of another quantity is possible in the IDV. 
> In the Displays, you can select the 3D surface, and then Vector Over 
> Topography. When the new window popup, you need to use Formula > Misc > 
> Change Unit, and then select the variable like potential temperature, the 
> trick is to use the change unit formula since the unit of topography need to 
> be convertible to the unit of height.
> 
> Yuan,
> 
> I'm not sure that I understand two aspects of this approach:
> 
> (1) Where does the IDV get the height information that describes the 
> elevation of the isosurface (of, say, potential temperature)? In following 
> the procedure that you outline above, I'm not prompted for a particular value 
> of potential temperature (say) that defines the isosurface in z-space (and, 
> implictly, the height field for that surface), and if there is a default 
> choice, then I'm not sure what it might be. There was a default pressure 
> level selected for the wind information, though (1000 mb), and changing that 
> level changes the position of the isosurface in space on which the vectors 
> are plotted--lower values raise the level of the isosurface, which behaves 
> like pressure surfaces, whereas lower values of potential temperature would 
> produce surfaces lower and lower in the atmosphere.
> 
> I have to narrow the vertical scale to 300-350 meters before I see much 
> vertical relief in whatever surface the wind vectors are plotted on.
> 
> Bottom line here: I don't know what surface the wind vectors are being 
> plotted on. I can plot a potential temperature isosurface by itself on the 
> same display, and its shape doesn't resemble that of the surface on which the 
> winds are plotted.
> 
> (I've attached a bundle to illustrate.)

Hi Dave,
      I was wrong, I did not pay much attention to the isosurface. So the 
answer should be no to your previous second question. The vector display in the 
IDV is 2D, and the iso surface is 3D, I can not picture it in my mind how and 
why to plot it this way.

> 
> (2) After selecting Formula > Misc > Change Unit, I'm presented with a dialog 
> box the prompts me to enter the name and unitSpec properties of some value 
> (to be selected subsequently and that will serve as the topography--in my 
> case, potential temperature). What function do these two pieces of 
> information serve? Since they aren't presented from a menu (I have to type 
> them manually), it seems as if they might serve only a labeling function. In 
> any case, I entered "Potential Temperature" for the "name" property and 
> "meters" for the "unitSpec" property. (Specifying "Kelvins" for the 
> "unitSpec" property produced an error down the road: "topography units K must 
> convertible with m or gpm".)
> 
> An unrelated question: Does the IDV plot isogons (contours of wind direction) 
> from model data? I don't see it on the list of derived quantities. I started 
> writing a Jython library procedure to calculate it, but discovered that my 
> Jython programming ability isn't up to that task yet--maybe I'll try again 
> when I've got more time, but I should first poll the IDV user community to 
> see if someone has already done this.
> 
This should be doable, and there is a java function available in the IDV. I 
will let you know tomorrow when I get the chance to dig into the source code.

Yuan
> -- Dave
> 
> 
> 


Ticket Details
===================
Ticket ID: MUS-211252
Department: Support IDV
Priority: Normal
Status: Open