[ncl-talk] "Noise" when plotting station data

[Mary Haley]

Hi Meina,

The "streaking" that's occurring I think is because when you plot random
data using NCL, it is trying to smooth the data by default, using a
non-convex polygon that encloses all your data points.

Try drawing raster contours instead, by setting:

  res at cnFillMode = "RasterFill"     ; draw raster contours instead of
smoothed contours

If you want to mask all areas except California, see example mask_8.ncl
which is similar:

http://www.ncl.ucar.edu/Applications/mask.shtml#ex8

I think in your case you could set:

  res at mpDataBaseVersion           = "MediumRes"
  res at mpFillAreaSpecifiers        = (/"Land", "California","Water"/)
  res at mpSpecifiedFillColors       = (/"white","transparent","white"/)
  res at cnFillDrawOrder             = "PreDraw"  ; Make sure map fill happens
                                               ; last.

I will update the station_1 example to reflect the difference b/w smooth
and raster fill.


--Mary




On Tue, Jul 11, 2017 at 9:00 PM, Meina Wang <mnawang at ucdavis.edu> wrote:

> Dear NCL users:
>
> I ran into a problem when trying to use the function gsn_csm_contour_map_c
> e to plot station data (with latitude and longitude).  I followed this
> example  <https://www.ncl.ucar.edu/Applications/Scripts/station_1.ncl>form
> NCL website and got the figure with "noise" over region where there is no
> input data point (over Nevada).  The plot is attached below, with black
> dots showing the data points, and color contour underneath is plotted from
> gsn_csm_contour_map_ce function, so there is no data over Nevada, while
> the function still extrapolate values over there.
>
> Below are the main res setting for plotting station data:
>
>   res at sfXArray                    = lons
>
>   res at sfYArray                    = lats
>
>
>   plot=gsn_csm_contour_map_ce(wks,w,res1)
>
>
> Has any one had this problem before?  Any thoughts or suggestion is much
> appreciated!  Thank you.
>
> ​Best,
> Meina
>
> --
> Meina Wang
> PhD candidate in Atmospheric Science
> Department of Land, Air and Water Resources
> University of California, Davis
> Davis, CA 95616
>
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