[gradsusr] Better polygon shapefiles

[Jennifer M Adams]

On Jan 18, 2016, at 3:56 PM, Michael Mase <masester at gmail.com<mailto:masester at gmail.com>> wrote:

Thanks, Jennifer! This is very helpful. I'm interested to learn more why GrADS can't export with rings.
http://cola.gmu.edu/grads/gadoc/shapefiles.html#caveat
—Jennifer



I've used degrib a few times and it seems to do this beautifully. However, it relies on the GRIB data being in the final state - which makes GrADS more appealing.
On Mon, Jan 18, 2016 at 3:52 PM Jennifer M Adams <jadams21 at gmu.edu<mailto:jadams21 at gmu.edu>> wrote:
The polygons in a Grads-generated shapefile conform to the ESRI specifications (https://www.esri.com/library/whitepapers/pdfs/shapefile.pdf) but have an additional constraint so that GrADS will render them properly: no rings, a.k.a. polygons within other polygons, a.k.a. “donuts". For this reason, the filled contours are are sliced up into odd-looking polygons that you can see clearly if you draw them individually, or with an outline color that does not match the fill color. There is nothing to be done about that on the GrADS side. There are probably some GIS tools that will merge polygons, but if you want a smooth-looking and outlined filled contour plot, write out the polygons and line contours into two separate shapefiles and overlay them. —Jennifer


On Jan 18, 2016, at 2:08 PM, Michael Mase <masester at gmail.com<mailto:masester at gmail.com>> wrote:

Exporting shapefiles works fantastic when using lines. However, when you export using polygons, you get very broken and disconnected shapes

Does anyone have any advice on writing/exporting solid shapefiles that have joined multi-polygons (for each contour region; each temperature interval, for example)?

It would be nice if each polygon layer represented each interval on the map and was nicely joined and closed properly.
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Jennifer M. Adams
Center for Ocean-Land-Atmosphere Studies (COLA)
111 Research Hall, Mail Stop 2B3
George Mason University
4400 University Drive
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Jennifer M. Adams
Center for Ocean-Land-Atmosphere Studies (COLA)
111 Research Hall, Mail Stop 2B3
George Mason University
4400 University Drive
Fairfax, VA 22030


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