[ncl-talk] RasterFill and MissingValFill

[Evelyn Grell - NOAA Affiliate]

Thanks so much, Adam and Dave, for the clear explanations and the
work-around!

- Evelyn

On Fri, Nov 20, 2015 at 10:44 AM, Adam Phillips <asphilli at ucar.edu> wrote:

> Hi Evelyn,
> Dave is exactly correct in what is going on here. The contouring/shading
> for the missing areas are being drawn correctly regardless of the setting
> of cnFIllMode. The missing value perimeter line is being drawn at the
> center of the grid cells *next to* grid cells set to _FIllValue
> regardless of the setting of cnFIllMode. When you set cnFillMode =
> "RasterFill" NCL does not need to look at neighboring grid cells for
> shading and can shade the whole cell, thus decreasing the shaded missing
> areas.
>
> The question then is should NCL change the position of the missing value
> perimeter line depending on the setting of cnFillMode? That would likely
> create as many questions as the current set up.
>
> Thanks for sending a short easy-to-read script and your data files. That
> always makes testing things easier. I do have a solution for you. I created
> a second plot where cnFillColor is set to transparent and cnFillMode =
> "AreaFill". Thus, the only aspect of the original plot being drawn is the
> missing value shading and perimeter line. I then overlay this plot on the
> original plot. See the attached script and resulting output graphic. Note
> that if you are going to frequently switch between a setting of RasterFill
> and AreaFill it might be good to put the overlay plot coding into a
> user-defined function instead of an if statement like I did.
>
> Hope that all makes sense. If you have any questions let ncl-talk know.
> And thanks to Dave for chiming in and identifying what was going on.
> Adam
>
>
> On Thu, Nov 19, 2015 at 4:45 PM, Dave Allured - NOAA Affiliate <
> dave.allured at noaa.gov> wrote:
>
>> Adam,
>>
>> I think this is a very old issue; I have seen this before with
>> RasterFill.  Actually there IS a difference in how missing values are
>> shaded, and it is normal.  The problem is with the the perimeter lines, not
>> the missing value shading.
>>
>> Missing value areas are drawn correctly in both modes, it is just that
>> the area shaded for non-missing data is naturally larger in RasterFill mode
>> than in AreaFill mode.  RasterFill draws the normal shaded data areas an
>> extra 1/2 cell width into missing value regions.
>>
>> As far as I can remember, the missing value perimeter line has ALWAYS
>> followed edges as generated by AreaFill, regardless of alternate cnFillMode
>> settings.  I do not know whether there was ever any intention of changing
>> the perimeter line to follow the cnFillMode, or whether this was just a
>> feature intended only for normal AreaFill mode.  I did not find any clues
>> in ContourPlot documentation.  HTH.
>>
>> --Dave
>>
>>
>> On Wed, Nov 18, 2015 at 4:45 PM, Adam Phillips <asphilli at ucar.edu> wrote:
>>
>>> Hi Evelyn,
>>> There should not be any difference in how the missing values are shaded.
>>> Can you send us a simplified version of your script and data files so we
>>> can take a look?  If the data files are too big to send over ncl-talk you
>>> can use our ftp site:
>>> http://www.ncl.ucar.edu/report_bug.shtml#HowToFTP
>>> Also, please let us know what version of NCL you are using..
>>> Adam
>>>
>>> On Tue, Nov 17, 2015 at 2:50 PM, Evelyn Grell - NOAA Affiliate <
>>> evelyn.grell at noaa.gov> wrote:
>>>
>>>> Hi,
>>>>
>>>> I am plotting cross-sections and was filling the area below ground with
>>>> a gray fill, more or less representing the terrain.  This seemed to be
>>>> working fine until I plotted a field using cnFillMode  = "RasterFill".  In
>>>> that case, the "missing" perimeter line is in the same place, but the gray
>>>> fill does not cover the entire area under the perimeter line.  See attached
>>>> plots.
>>>> Since I would like to compare plots -- some with rasterfill and some
>>>> with the default areafill, it is awkward to explain why the terrain looks
>>>> different.  Is there a way around this?  I can remove the perimeter line,
>>>> but the gray-filled area is different.
>>>>
>>>> Relevant resources:
>>>>
>>>>      res at cnMissingValPerimOn     = True
>>>>      res at cnMissingValFillColor   = "gray"
>>>>      res at cnMissingValFillPattern = 0
>>>>
>>>> The only difference between plots is whether this line is used:
>>>>      resDBZ at cnFillMode      = "RasterFill"
>>>>
>>>> Thanks,
>>>> Evelyn
>>>>
>>>
>
>
> --
> Adam Phillips
> Associate Scientist,  Climate and Global Dynamics Laboratory, NCAR
> www.cgd.ucar.edu/staff/asphilli/   303-497-1726
>
> <http://www.cgd.ucar.edu/staff/asphilli>
>
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