[ncl-talk] Small issue plotting highways

Wed Jun 23 16:02:20 MDT 2021

Sure go ahead and share if you like.

On Wed, Jun 23, 2021 at 5:21 PM Bassill, Nicholas <nbassill at albany.edu>
wrote:

> Hi Andrew, all,
>    Sort of a shot in the dark here, but coincidentally, I also regularly
> make radar plots and overlay highways (also in gray), along with a whole
> bunch of other info and I have not noticed this with my png files. I also
> use a shapefile for the highways and more or less use your technique I
> think. I'm attaching two examples - one from an active day, and one from
> today just to demonstrate that I always see the same road behavior. I see
> your line thickness is very small - perhaps increasing the thickness would
> help a bit?
>
> If you'd like I'd be happy to share this script, though fair warning it
> has a ton of stuff in so may be a bit hard to parse.
>
>
> Nick Bassill, PhD
>
> Director of Research & Development, Center Of Excellence
>
> Affiliated with NYS Mesonet
>
> LC SB-28, 1400 Washington Ave.,
>
> SUNY, University at Albany, NY 12222
> Contact: (518) 442-6375 | @NickPBassill |
> http://operations.nysmesonet.org/~nbassill/
> ------------------------------
> *From:* ncl-talk <ncl-talk-bounces at mailman.ucar.edu> on behalf of Dave
> Allured - NOAA Affiliate via ncl-talk <ncl-talk at mailman.ucar.edu>
> *Sent:* Wednesday, June 23, 2021 4:52 PM
> *To:* Andrew Kren - NOAA Federal <andrew.kren at noaa.gov>
> *Cc:* ncl-talk <ncl-talk at ucar.edu>
> *Subject:* Re: [ncl-talk] Small issue plotting highways
>
> Andrew, the difference between your plots with and without the contour
> fill layer is surprising.  I can only speculate that there might be a
> branch somewhere inside NCL, that handles antialiasing differently,
> depending on which graphics layers are active.  Notice that the resolution
> of the lettering is also affected slightly.
>
> I still think your best bets are to try the resource suggested by Rick, or
> to avoid the issue by using some form of vector graphics for output.
> Thanks for showing that contrasting plot, and good luck.
>
>
> On Wed, Jun 23, 2021 at 8:08 AM Andrew Kren - NOAA Federal <
> andrew.kren at noaa.gov> wrote:
>
> Thanks Dave and Rick. I will try that. Here is what I get on a day when
> there is nothing on the radar to plot. The highways show up just fine with
> no changes to the code. I'm wondering if it has something to do with the
> contours overlaid or something similar? I will also try a PDF or PS file.
>
>
> On Tue, Jun 22, 2021 at 6:31 PM Dave Allured - NOAA Affiliate <
> dave.allured at noaa.gov> wrote:
>
> Andrew, PNG is an image format that naturally consists of a grid of
> pixels.  The only pixellation that I see in your plot is the natural pixels
> in the PNG format.  Your highways are mostly very fine diagonal lines.  PNG
> decomposes a diagonal line into a group of small gray and black squares
> (pixels) on a regularly spaced pixel grid.  When the intended line is thin
> enough, it is difficult to get a clear representation on the pixel grid.
> One of the possible results is apparently dashed lines like those I am
> seeing.
>
> Try making the same plot using vector graphics such as PDF, postscript
> (PS), or SVG, as Rick suggested.  These vector formats preserve a true
> mathematical representation of line data.  The result is clean edges and
> fine lines that will not pixellate when you zoom in, when using proper
> viewing software that supports true vector mode display.
>
>
> On Tue, Jun 22, 2021 at 12:15 PM Andrew Kren - NOAA Federal via ncl-talk <
> ncl-talk at mailman.ucar.edu> wrote:
>
> Thanks, I'll check it out.
>
> On Tue, Jun 22, 2021 at 11:25 AM Rick Brownrigg <brownrig at ucar.edu> wrote:
>
> Hi Andrew,
>
> It's odd that you are getting inconsistent results. Do you see the same
> thing if you write to a PS or PDF file? I don't know what's going on, but
> it looks like a  bit of overzealous anti-aliasing. There's a resource to
> control whether antialiasing is applied or not:
>
> https://www.ncl.ucar.edu/Document/Graphics/Resources/wk.shtml
>
> It's on by default and generally yields better results, but you might
> experiment with it.
>
> Wish I had a better answer.
> Rick
>
>
> On Tue, Jun 22, 2021 at 8:45 AM Andrew Kren - NOAA Federal via ncl-talk <
> ncl-talk at mailman.ucar.edu> wrote:
>
> Hi there,
>
> I am plotting radar data and overlaying highways onto the map. I first
> plot the radar analysis, then overlay the highway information by
> reading/plotting the shapefile.
>
> At times, when I view the PNGs, the highways show up as blotched out (lack
> of detail and pixelated; see attached image). At other times, the highways
> show up very clear and darker as expected. Is there a reason for this?
> Below shows a snippet of my code that produces the radar plot and the
> highway overlay.
>
>  plot = gsn_csm_contour_map(wks,radar,res)
>
>  ; add highway polylines to the map from shapefile
>  plres = True
>  plres at gsLineColor = "grey48"
>  plres at gsLineThicknessF = 0.2
>  id =
> gsn_add_shapefile_polylines(wks,plot,SHAPE_DIR+"roadtrl020.shp",plres)
>
> Thanks,
>
> --
>
> Andrew Kren
> Meteorologist
> NOAA's National Weather Service
> Raleigh Forecast Office
> 1005 Capability Drive, Suite 300
> Raleigh, North Carolina 27606
> voice: 919-326-1035
> mailto: andrew.kren at noaa.govhttp://www.weather.gov/rah
>
>

-- 

Andrew Kren
Meteorologist
NOAA's National Weather Service
Raleigh Forecast Office
1005 Capability Drive, Suite 300
Raleigh, North Carolina 27606
voice: 919-326-1035
mailto: andrew.kren at noaa.govhttp://www.weather.gov/rah
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