[ncl-talk] issue with gsn_add_polygon

[Dave Allured - NOAA Affiliate]

Very nice plots.  Notice how those mystery lines fade as they approach
(0,0).  That is because they are polygons, not lines.  Specifically, long
skinny triangles.  That is a clue.

xib and yib are not closed contours.  I am not sure whether gsn_add_polygon
is supposed to close them for you.  But since this seems to coincide
with the visible anomalies, try closing them explicitly.

    xib = new( (/2*nbins+1/), "double")
    yib = new( (/2*nbins+1/), "double")
    ...
    xib(2*nbins) = xib(0)
    yib(2*nbins) = yib(0)


On Fri, Jun 12, 2020 at 7:59 PM Adam Herrington via ncl-talk <
ncl-talk at mailman.ucar.edu> wrote:

> I'm attempting to compute a raw violin-type plot. This is similar to a box
> plot, but I'm drawing a polygon around the pdf, and I close the polygon
> through a mirror image (-1*probability). Then I rotate it so it's vertical,
> and align it with the x-axis "id" of the box plot.
>
> If you're not following, I don't blame you ... this is hard to describe.
> Attached is my attempt at this that will hopefully clarify what I'm trying
> to do.
>
> **digression before I go on to details on my primary issue**
> I'd like to experiment with an actual violin plot, with a smoothed kernel
> density estimate of the distribution. The routine kde_n_test
> <https://www.ncl.ucar.edu/Document/Functions/Built-in/kde_n_test.shtml> should
> work, but the warnings on the ncl page say the function is under
> construction. Is that the latest update for this function?
> **end digression**
>
> You'll notice for panels 2 and 3 there is a line pivoting from the bottom
> of the pdf's to the (0,0) point on the plot. I'm having trouble tracking
> down why this occurs and how to fix it. I'm going to copy-paste the
> relevant portions of the code for one of the x-value id's.
>
>   dx = 0.4d0 ;; x-depth of the pdf
>   xvals = (/1.,2.,3.,4.,5.,6./) ;; case id
> ...
>     pdfib = pdfx(ibdiff,nbins,optpdf)
>     pdfib = pdfib/max(pdfib)
>
>     xib = new( (/2*nbins/), "double")
>     yib = new( (/2*nbins/), "double")
>
>     xib(0:nbins-1) = xvals(n) - dx*pdfib
>     xib(nbins:2*nbins-1) = xvals(n) + dx*pdfib(nbins-1:0)
>     yib(0:nbins-1) = pdfib at bin_center
>     yib(nbins:2*nbins-1) = pdfib at bin_center(nbins-1:0)
>
>     pgstr = unique_string("dum")
>     plot@$pgstr$ = gsn_add_polygon(wks,plot(0),xib,yib,respg)
>
> I am pretty sure the xib and yib are a closed contour.. they go from
> 0:nbins-1 and then nbins:2*nbins-1 ... Would like to get another set of
> eyes on this though
>
> thanks,
> Adam
>
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