[gradsusr] set shp -poly

[Yaqiang Wang]

It seems GrADS does not form real 'polygon' from contour lines by
topology analysis. This is the source of the problem.

On Wed, Jan 4, 2012 at 7:17 AM, Jennifer Adams <jma at cola.iges.org> wrote:
> Jeff,
> The shapfile interface in GrADS creates a shapefile that contains polygons
> that fill out the areas outlined by the shaded contours. Because of the
> rules in the shapefile spec regarding polygon geometry, the area inside a
> shaded contour is split up into many pieces so that individual polygons do
> not overlap and do not contain holes (no donuts). That is why you are seeing
> all the vertical lines. If you color in the polygons and use the same color
> to draw the outline, you won't see the vertical lines and the plot will look
> more normal (like the shaded contour plot in GrADS).
>
> Also, before you create the shapefile, you must be in the latlon projection
> (set mproj latlon). No other projection will work. It should be possible to
> use your GIS tool to re-project the data in the shapefile using the metadata
> in the file provided by GrADS. From the attachement you sent, it's difficult
> to tell what the problem is -- better to draw a plot of a variable such a
> land mask that would clearly show whether the boundaries in the data are
> lining up with the political boundaries (and color them in and use matching
> outline color). If there is an issue in the way Qgis is re-projecting the
> shapefile, then that may or may not be a GrADS problem.
>
> The polygons 'connect to the outside' because they are filling in the
> lat/lon block defined by your dimension environment. You can't mask your
> shapefile according to political boundaries, but you can choose to not draw
> a certain contour level by using -1 instead of a color number in the 'set
> ccols' command.
>
> I can't help you any further without more specific information about what
> version of GrADS you're using, what the descriptor file looks like for your
> data, the source of your data file (so I can grab a sample), what your
> commands were to generate the shapefile, and what you did inside Qgis to
> create the display in your attachment.
> --Jennifer
>
>
>
>
> On Jan 3, 2012, at 4:22 PM, Jeff Lake wrote:
>
> I believe there is a minor, okay major, flaw in the conversion to shape file
> here is the shape file I get when converting the RTMA GRIB over (see
> attachment)
> the resulting polygons all 'connect' to the outside
> this is a cint set from -30 to 140 by 5 degree's
> this is a better result then another piece of software, but still not
> correct..
>
> anybody got suggestions ??
>
> --
> -Jeff Lake
> MichiganWxSystem.com
> WeatherMichigan.net
> TheWeatherCenter.net
> GRLevelXStuff.com
>
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>
> --
> Jennifer M. Adams
> IGES/COLA
> 4041 Powder Mill Road, Suite 302
> Calverton, MD 20705
> jma at cola.iges.org
>
>
>
>
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-- 
*************************************************
Dr. Yaqiang Wang
Chinese Academy of Meteorological Sciences (CAMS)
46, Zhong-Guan-Cun South Avenue
Beijing, 100081
China

yaqiang.wang at gmail.com

http://www.meteothinker.com
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