[ncl-talk] gc_inout; problem with polygons over equator & zonal extent > 180 degr

[Devries, Andries]

Dear NCL users/developers,

I ran into a problem with ncl (v.6.3.0) using the function gc_inout. I used the function to identify grid points on a gaussian grid (512x256) within a polygon. When the polygon has a zonal extent larger than 180 degrees and extends over the equator (covers partly both northern and southern hemispheres), a problem occurs; on the edges gridpoints are missing that should have been identified.

I attached 2 simple idealized plots that demonstrate the issue; all gridpoints should be identified within the boxes:
plot1) box lon-100:100, lat 10:30; everything fine
plot2) box lon-100:100, lat -10:10; gridpoints on both edges are missing

Is this a bug or a known issue as the description of gc_inout says: "and that the vertices can be contained in a hemisphere"?

Any suggestions how can I work around this issue?

Looking forward to suggestions!
Cheers,
Andries
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