[ncl-talk] Possible bug in plots of unstructured grids

[Mathieu Dutour]

Thank you,
Yes, with those modifications the result is satisfying.

  Mathieu

On Wed, Dec 17, 2014 at 2:15 AM, David Brown <dbrown at ucar.edu> wrote:
>
> I agree that something odd is happening when you try to plot this data
> using the 'ele' array in the file to define the triangulation.
> However, I was able to plot it quite easily using NCL's built-in
> triangulation code. The only change I needed to make from your
> original code is to comment out the lines:
>
>   ; res2 at sfElementNodes      = f->ele
>  ; res2 at sfFirstNodeIndex    = 0
>
> For the plot I am attaching I also changed
>
> res2 at mpDataBaseVersion      = "MediumRes"
>
> because the high res data does not work well for global plots.
>
> We will need to investigate why the explicit triangulation in your
> data set causes a problem. But you can get a better plot faster by not
> setting
> sfElementNodes and letting NCL compute the triangulation.
>
> Hope this helps.
>  -dave
>
>
> On Tue, Dec 16, 2014 at 10:24 AM, Mathieu Dutour
> <mathieu.dutour at gmail.com> wrote:
> > Dear all,
> >
> > I would like to plot some unstructured grid that encompass all
> > the oceans of the world.
> >
> > There are two obstacles to that. One is the periodicity in longitude
> > and the other is the singularity at the south and north pole. The
> > singularity can be avoided by removing points with latitude not
> > in acceptable range. The periodicity can be treated by removing
> > the points of longitude +-180.
> >
> > A priori, the drawing should then proceed correctly, but it does not.
> > The grid I put as input passes all the sanity checks I can think of.
> > What makes me think that there is a bug is that if I restrict to
> > positive latitudes (0<lat<90) or negative latitude (-90 < lat < 0) then
> > the drawings are ok but it is not when I put everything together.
> >
> > All relevant files for debugging are available in
> > http://mathieudutour.altervista.org/Sending/PLOT_globunstruc.tar.gz
> > The reduction technique from WholeWorld ---> UpperLatitude, LowerLatitude
> > is to remove the points of noncorrect latitude and any triangle that
> > contain them.
> >
> > The three pictures are
> > http://mathieudutour.altervista.org/Sending/LowerLatitude.png (good)
> > http://mathieudutour.altervista.org/Sending/UpperLatitude.png (good)
> > http://mathieudutour.altervista.org/Sending/WholeWorld.png (bad)
> >
> > Thank you in advance for any help in the debugging and please ask
> > if I can help you.
> >
> > Best,
> >
> >   Mathieu
> >
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>
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