Non-uniform grids and triangular mesh conversion
The ARPEGE grid used in the examples on this page is a non-uniform grid. It was given to us by Christophe Cassou from the Centre National de la Recherche Scientifique (CNRS/CERFACS) in Toulouse. This grid is rotated with respect to the globe so as to put its poles somewhere other than at the North and South Pole.
It is better to convert this grid to a triangular mesh rather than interpolate it to a uniform grid before contouring. Note that only contouring is available with triangular mesh conversion at this time.
If the input array to a gsn_csm graphical interface is one- dimensional, and also has one-dimensional lat/lon arrays of the same length, NCL automatically uses triangular mesh conversion. The lat/lon information must be provided by setting sfXArray and sfYArray.
For more information on non-uniform grids that NCL can handle, see the document "Non-uniform grids that NCL can contour."