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

[Mathieu Dutour]

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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