[ncl-talk] Missing color fill with fixed contour levels

[David Brown]

There was a check-in on 2015-06-24 that addressed this problem with
this explanatory text:

r16255 | dbrown | 2015-06-24 17:02:16 -0600 (Wed, 24 Jun 2015) | 8 lines

NCL-2236: partial fix for constant fill with AreaFill mode set

This works a bit better than the original hack but it is not yet
totally reliable.
It may not work when the data field is bigger than the area displayed within the
viewport (i.e. over a map when the view is limited using map limits
rather than by
sub-setting the data).

======

Note that the AreaFill method was not originally designed to work when
there are no isolines within the visible area of the plot. The fix can
still theoretically fail but it should be much better than the
previous situation.
 -dave


On Thu, Dec 31, 2015 at 9:51 AM, Rick Brownrigg <brownrig at ucar.edu> wrote:
> Hi Dave,
>
> I get the same blank map running your script using 6.3.0 on yellowstone.
> However, running your script unmodified using a current development snapshot
> of the code, I get a correctly filled, mono-colored map (attached).  So the
> issue appears to have cropped up before and has been fixed -- I don't know
> the details.
>
> Do you need a binary of the development branch -- its usually quite stable?
>
> Rick
>
>
> On Wed, Dec 30, 2015 at 6:25 PM, Dave Allured - NOAA Affiliate
> <dave.allured at noaa.gov> wrote:
>>
>> NCL team,
>>
>> I am making ordinary color filled contour maps of gridded data, with fixed
>> contour levels.  When all data values lie between two adjacent contour
>> levels, all one color is expected.  However, NCL 6.3.0 fails to color fill
>> in these cases.  The result is all white maps that interrupt presentation
>> sequences.
>>
>> Attached plot #1 shows color fill forced by adding an intermediate contour
>> level.  Plot #2 shows the problem, a blank plot when fewer contour levels
>> are selected, and all one color expected.
>>
>> Here is the script for plot #2, the non-filled map.  Plot #1 results by
>> changing cnLevelSpacingF to 6 instead of 12.  The input file is in the third
>> attachment:
>>
>> begin
>>   f = addfile ("data.no-color.nc", "r")
>>   dat = f->dat
>>   print ("Data range of full grid = " + min (dat) + ", " + max (dat))
>>
>>   wks = gsn_open_wks ("x11", "plot.test")
>>   res                      = True
>>   res at cnFillOn             = True
>>   res at cnConstFEnableFill   = True
>>
>>   res at cnLevelSelectionMode = "ManualLevels"
>>   res at cnMinLevelValF       = 0
>>   res at cnMaxLevelValF       = 24
>>   res at cnLevelSpacingF      = 12   ; smaller generates color fill
>>
>>   res at mpMinLonF    = 234     ; any boundary outside data limits
>>   res at mpMaxLonF    = 260     ; generates color fill
>>   res at mpMinLatF    = 31
>>   res at mpMaxLatF    = 50
>>
>>   res at mpCenterLonF = (res at mpMinLonF + res at mpMaxLonF) / 2.0
>>   res at gsnAddCyclic = False
>>   res at mpFillOn     = False
>>   res at mpOutlineBoundarySets = "AllBoundaries"
>>
>>   plot = gsn_csm_contour_map_ce (wks, dat, res)
>> end
>>
>> Please note that two different kinds of changes result in correct color
>> fill, just not all one color which is what I need.  You can decrease
>> cnLevelSpacingF to some value such as 6, which generates more than one
>> color.  You can also change any of the map border resources (mpMinLonF etc.)
>> to extend outside the data limits, resulting in missing values along the
>> edges showing as blank (white) areas.
>>
>> Both of these changes have something in common.  They all result in at
>> least one color variation inside the plot frame.  The failure occurs when
>> the entire plot frame should be one solid color with no breaks for missing
>> values or contour lines.
>>
>> Is this a bug in NCL?  Is there an existing solution?  Can you please
>> either change NCL to prevent this kind of blanking, or else add a resource
>> similar to cnConstFEnableFill, to allow users to control the blanking in
>> such cases?  Thanks for your consideration.
>>
>> --Dave
>>
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>
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