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Due to the current gap in continued funding from the U.S. National Science Foundation (NSF), the NSF Unidata Program Center has temporarily paused most operations. See NSF Unidata Pause in Most Operations for details.
I cannot speak for VisAD, however in McIDAS the algorithm for drawing
streamlines is the one described in: Monthly Weather Review: Vol.
105, No. 6, pp. 786–788.
The "density" value is used to determine in what grid "boxes"
streamlines can start. Highest density says that a streamline will
start in every grid box and be drawn to its termination (rules for
stopping drawing are described in the paper). Streamlines are always
started in the center of a grid box, thus no more than one will ever
be started in a box -- that does not, of course, prevent more than one
streamline from passing through a grid box.
Hope that helps.
tom
On 3/29/06, James Kelly <J.Kelly@xxxxxxxxxx> wrote:
> Hi,
>
> I've been looking at the quality of streamline analyses (of atmospheric
> wind fields) lately.
>
> I was experimenting with streamline displays in the McIDAS system, and
> thought (IMHO) that the streamline analyses looked better as the density
> of the streamlines increased.
>
> I then tried to increase the density of the streamlines in a visad
> display, and but wasn't able to generate the same density as the McIDAS
> display.
> Should I be able to do this? If so how?
>
> Tried changing "streamlineDensity" from the default of 1.0 to higher
> values of 10.0, 100.0, 1000.0 and 1000.0, but didn't notice much change
> beyond 100.0.
>
> Further details:
> 1) In McIDAS I did this:
> GRDDISP <modelname> FHOUR=0 PARAM=STREAML LEV=SFC LAT=-20 20 LON=-160
> -100 CINT=0 COLOR=15
>
> Image is attached as "mcidas_streamline.png"
>
> 2) In Visad/jython I did this:
>
> maps = (xMap, yMap, rngUMap, rngVMap)
>
> disp = subs.makeDisplay(maps)
> flowcontrol = rngUMap.getControl()
> flowcontrol.enableStreamlines(TRUE)
> strmDensity = flowcontrol.getStreamlineDensity()
> stepFactor = flowcontrol.getStepFactor()
> flowcontrol.setStreamlineDensity(10000.0)
> print " streamline density " , strmDensity, " stepFactor ", stepFactor
>
> drLAPSuv=subs.addData("windbarbs", uv, disp)
>
> Image is attached as "visad_streamline.png"
>
> Cheers,
>
> James
>
>
> --
> James Kelly
> Australian Bureau of Meteorology
>
>
>
>
>
--
Tom Whittaker
University of Wisconsin-Madison
SSEC/CIMSS
1225 W. Dayton Street
Madison, WI 53706 USA
ph: 608-262-2759
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