[ncl-talk] wind vector

Xi Chang xi.chang01 at gmail.com
Thu Dec 11 13:56:54 MST 2014 

Ok,,well then,  I will not use the "curly'" mode for my journal submission
to AMS :(
I hope that NCL team can figure out this issue soon. Thank you,

Chang.

On Thu, Dec 11, 2014 at 6:39 PM, David Brown <dbrown at ucar.edu> wrote:

> Well, again, without seeing your code or your plot, it is hard to say
> for sure, but that is probably because of the different nature of the
> algorithm used to draw curly vectors vs. regular straight vectors.
> Even though a curly vector starts at a particular grid point, its
> progress is influenced by the values at the nearby grid points. The
> approach I suggested yesterday makes grid points below the minimum
> value into missing value areas, potentially causing more vectors to be
> eliminated than you would like, or changing the way they progress. So
> I agree that it is not really the same behavior as vcMinMagnitudeF
> would have. Unfortunately I do not know of any other way around your
> difficulty. Sorry.
>  -dave
>
>
> On Wed, Dec 10, 2014 at 11:47 PM, Xi Chang <xi.chang01 at gmail.com> wrote:
> > Thanks guys,
> > Im using this a work-around prior to plot the vector,
> >
> > u = where(sqrt(u*u + v * v) .lt. min_magnitude, u at _FillValue, u)
> > v = where(sqrt(u*u + v * v) .lt. min_magnitude, v at _FillValue, v)
> >
> > but the results are not the same as the use of  res at vcMinMagnitudeF
> > thanks
> >
> > On Wed, Dec 10, 2014 at 8:47 PM, David Brown <dbrown at ucar.edu> wrote:
> >>
> >> Kyle is definitely correct in saying that "curly vectors are more akin
> >> to streamlines". In fact at the low level, a modified version of the
> >> streamline code is used to implement them. That is also why the
> >> vcMinMagnitudeF is not currently enabled for curly vectors. However,
> >> since each curly vector originates from a specific grid point where a
> >> single vector magnitude can be computed, it seems to me that there is
> >> nothing to prevent vcMinMagnitudeF from being supported for curly
> >> vectors. Whether it will produce a good looking result or not is
> >> another question.
> >>
> >> A work-around might be to use the "where" function, with your
> >> user-defined min_magnitude:
> >> u = where(sqrt(u*u + v * v) .lt. min_magnitude, u at _FillValue, u)
> >> v = where(sqrt(u*u + v * v) .lt. min_magnitude, v at _FillValue, v)
> >>
> >> before plotting. Let us know if you have problems getting this to work.
> >>
> >> I will create a ticket for implementing vcMinMagnitudeF for curly
> vectors.
> >>  -dave
> >>
> >>
> >>
> >>
> >> On Wed, Dec 10, 2014 at 7:50 AM, Kyle Griffin <ksgriffin2 at wisc.edu>
> wrote:
> >> > I'm not Dave, but I'll go ahead and say "no" - CurlyVectors are more
> >> > akin to
> >> > streamlines in that they don't exist at any one "point" but rather get
> >> > longer and turn with the wind as magnitude increases. You can't simply
> >> > turn
> >> > off the CurlyVector in some areas as it would break up the streamline
> by
> >> > falling below an arbitrary magnitude. vcMinMagnitude seems to look the
> >> > best
> >> > with either LineArrow or FillArrow glyphs, in my experience.
> >> >
> >> > Good luck!
> >> >
> >> >
> >> > Kyle
> >> >
> >> > ----------------------------------------
> >> > Kyle S. Griffin
> >> > Department of Atmospheric and Oceanic Sciences
> >> > University of Wisconsin - Madison
> >> > Room 1421
> >> > 1225 W Dayton St, Madison, WI 53706
> >> > Email: ksgriffin2 at wisc.edu
> >> >
> >> > On Wed, Dec 10, 2014 at 7:04 AM, Xi Chang <xi.chang01 at gmail.com>
> wrote:
> >> >>
> >> >> Hi Dave, HI NCL,
> >> >>
> >> >> so, is there any way around how to use " res at vcMinMagnitudeF  " for
> >> >> "CurlyVector" mode?
> >> >> Thanks
> >> >>
> >> >> chang.
> >> >>
> >> >> On Fri, Nov 7, 2014 at 3:22 PM, David Brown <dbrown at ucar.edu> wrote:
> >> >>>
> >> >>> Try turning off the curly vectors. It's possible that it hasn't been
> >> >>> enabled for that glyph style.
> >> >>>  -Dave
> >> >>>
> >> >>>
> >> >>> On Friday, November 7, 2014, Xi Chang <xi.chang01 at gmail.com> wrote:
> >> >>>>
> >> >>>> Thanks Dave,
> >> >>>>
> >> >>>> Anyway, nothing happens when I did as follows (the results are
> still
> >> >>>> the
> >> >>>> same):
> >> >>>>
> >> >>>>   res at gsnScalarContour      = True              ; vectors over
> >> >>>> scalars
> >> >>>>   res at vcRefMagnitudeF       = 20.0              ; vec magnitude
> >> >>>>   res at vcRefLengthF          = 0.06              ; size of ref
> vector
> >> >>>>   res at vcLineArrowColor      = "black"           ; white vectors
> >> >>>>   res at vcMinDistanceF        = 0.025              ; thins arrows
> near
> >> >>>> pole
> >> >>>>   res at vcGlyphStyle          = "CurlyVector"     ; turns on curley
> >> >>>> vectors
> >> >>>>   res at vcMinMagnitudeF       = 5
> >> >>>>
> >> >>>> On Fri, Nov 7, 2014 at 12:25 AM, David Brown <dbrown at ucar.edu>
> wrote:
> >> >>>>>
> >> >>>>>
> >> >>>>>
> >> >>>>>
> http://www.ncl.ucar.edu/Document/Graphics/Resources/vc.shtml#vcMinMagnitudeF
> >> >>>>>
> >> >>>>> On Thu, Nov 6, 2014 at 4:23 PM, Xi Chang <xi.chang01 at gmail.com>
> >> >>>>> wrote:
> >> >>>>> > Hallo, is there any trick to display wind vectors only for those
> >> >>>>> > whose
> >> >>>>> > magnitude greater than XXX m/s, bellow this values are not
> >> >>>>> > plotted.
> >> >>>>> > Im using
> >> >>>>> > a function called gsn_csm_vector.
> >> >>>>> >
> >> >>>>> > Thanks
> >> >>>>> >
> >> >>>>> > _______________________________________________
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> >> >>>>
> >> >>>>
> >> >>
> >> >>
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