[gradsusr] GrADS shapefile rings caveat

Michael Mase masester at gmail.com
Sat Sep 16 12:32:04 EDT 2017

Thanks, Jennifer. That makes sense. I'm wondering if there is a practical
way outside of GrADS to transform the exported shapefile to this desired
result. If you have any ideas, I would love to hear them. I may dig in to
see if I can find a practical way to do this and perhaps it could be added
as a hint to the documentation if you so wish.

Thanks again!


On Sat, Sep 16, 2017 at 11:24 AM Jennifer M Adams <jadams21 at gmu.edu> wrote:

> Hi, Mike —
> It is likely that the caveat will remain a feature in GrADS — even if we
> did not draw the inner rings, filling in the outer ring will always cover
> the entire area, and the area inside the inner rings could not be undrawn.
> A corrollary of the caveat is that shapefiles exported from GrADS will
> never have inner rings — the shading algorithm is specifically designed to
> avoid this problem. It would certainly have been easier to export closed
> contours as polygons with inner rings, but then GrADS would not have been
> able to display its own shapefiles properly.
> The workaround for the caveat is to rewrite the shapefile so that the
> polygons do not have inner rings; the boundary points would include the
> inner and outer rings with an overlapping line that connects the two rings.
> —Jennifer
> > On Sep 15, 2017, at 11:10 AM, Michael Mase <masester at gmail.com> wrote:
> >
> > Hi there,
> >
> > Just wondering if the latest GrADS version supports exporting shapefiles
> with inner rings now or if there are plans to support this in the future?
> >
> > Thanks,
> > Mike
> > _______________________________________________
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> > gradsusr at gradsusr.org
> > http://gradsusr.org/mailman/listinfo/gradsusr
> --
> Jennifer Miletta Adams
> Center for Ocean-Land-Atmosphere Studies (COLA)
> George Mason University
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