[ncl-talk] wind vector

[David Brown]

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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