[ncl-talk] Small issue plotting highways

Andrew Kren - NOAA Federal andrew.kren at noaa.gov
Thu Jul 1 13:13:48 MDT 2021 

I increased the thickness to 0.8 and it made the distortions less
noticeable. Thanks everyone!

On Thu, Jun 24, 2021 at 4:56 PM Dave Allured - NOAA Affiliate <
dave.allured at noaa.gov> wrote:

> Nick mentioned line thickness.  Yes, I think in the presence of this
> unwanted behavior, line thickness has *a lot* to do with it.  With
> thicker lines, the distortions may still be present, but will be much less
> noticeable.  Try gsLineThicknessF somewhere between 0.5 and 3.0.  This way,
> you may be able to keep using PNG format if you need to.
>
>
> On Thu, Jun 24, 2021 at 8:28 AM Andrew Kren - NOAA Federal via ncl-talk <
> ncl-talk at mailman.ucar.edu> wrote:
>
>> Thanks. I'm going to try the aliasing, and if that does not work, I'll
>> try the vector format. I have seen this issue with and without radar data
>> present on the map. Will keep you updated.
>>
>> On Thu, Jun 24, 2021 at 10:25 AM Rick Brownrigg <brownrig at ucar.edu>
>> wrote:
>>
>>> wks at wkAntiAlias = "Off"
>>>
>>> http://ncl.ucar.edu/Document/Graphics/Resources/wk.shtml
>>>
>>> I'm not sure aliasing is the issue, given your plots with/without radar
>>> data present. I would think things should be consistently good or bad. Have
>>> you tried a vector format as David suggested? If you need to post to a web
>>> page, SVG would be a great option as it scales nicely.
>>>
>>> Rick
>>>
>>> On Thu, Jun 24, 2021 at 8:18 AM Andrew Kren - NOAA Federal via ncl-talk <
>>> ncl-talk at mailman.ucar.edu> wrote:
>>>
>>>> Thanks! I tried that but it did not help. on the anti alias feature,
>>>> how do I set it? I did not see an example on the ncl documentation pages. I
>>>> tried this but it did not work. Thanks.
>>>>
>>>> wkAntiAlias(wks) = "Off"
>>>>
>>>> On Thu, Jun 24, 2021 at 9:24 AM Bassill, Nicholas <nbassill at albany.edu>
>>>> wrote:
>>>>
>>>>> The script can be found here:
>>>>> https://operations.nysmesonet.org/~nbassill/radar/radar.ncl . As I
>>>>> said, there's a lot of (fairly poorly commented) stuff going on there, but
>>>>> the most relatable lines for what you're doing are in the middle:
>>>>>
>>>>>    countyplot := gsn_csm_contour_map(wks2,newdata,resmap)
>>>>>
>>>>>    pres                 = True
>>>>>    pres at gsFillColor     = "transparent"
>>>>>    pres at gsFillOpacityF = 0.0
>>>>>    pres at gsEdgesOn = True
>>>>>    pres at gsLineThicknessF = 8.0
>>>>>    pres at gsLineColor= "gray40";"gray30"
>>>>>
>>>>>  ; if roads.eq."yes"
>>>>>    shpid = gsn_add_shapefile_polylines(wks2,countyplot,"tl_2015_36_prisecroads.shp",pres)
>>>>>  ; end if
>>>>>
>>>>> As I mentioned, my line thickness is much greater, though I'm not sure
>>>>> if that's the reason.
>>>>>
>>>>> Nick Bassill, PhD
>>>>>
>>>>>
>>>>>
>>>>> *From:* Andrew Kren - NOAA Federal <andrew.kren at noaa.gov>
>>>>> *Sent:* Wednesday, June 23, 2021 6:02 PM
>>>>>
>>>>> 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
>>>>>
>>>>>
>>>>>
>>>>> *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
>>>>>
>>>>> 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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