[ncl-talk] Contour fill transparency not working with RasterFill mode

[Mary Haley]

Hi Guido,

Thanks for providing your script and data offline.

The first thing to note is that cnMissingValFillColor will not be effective
in this case, because your data doesn't have any missing values.

The reason why you are not getting any transparency with raster fill is due
to a quirk with raster fill that I never knew about until Dave Brown helped
me look over your script today.

The simple fix is to replace this line:

 cmap_r(0,3)=0.0

with this line, which is setting the first color to black, but then making
it transparent:

 cmap_r(0,:)=0.0

Also, you can remove or comment this line, as it has no effect:

ResC at cnMissingValFillColor=0

Dave said he would look into why this quirk is necessary for raster fill
and maybe he'll post back here with an explanation.

Meanwhile, I'm going to update some of our examples to mention this so
hopefully the next user won't run into this.

Your ICON example is very nice by the way!  Would you be willing to let me
include it on our ICON examples page? If so, I may clean it up a little to
add some comments and to remove the "do" loop since this is only one file.
I won't redistribute the data file. You can email me offline about this if
desired.

--Mary







On Mon, Oct 2, 2017 at 9:44 AM, Mary Haley <haley at ucar.edu> wrote:

> I admit, I don't know what "the larger value" means in this case.  Dave
> would know, but I think he's out of the office for a few days. Did setting
> cnGridBoundFillColor fix anything?
>
> If not, is it possible for you to provide the script/data? You can do this
> offline if necessary. I don't think we have any unstructured examples like
> this that have missing data.
>
> Thanks,
>
> --Mary
>
>
>
>
> On Fri, Sep 29, 2017 at 9:47 AM, Karin Meier-Fleischer <
> meier-fleischer at dkrz.de> wrote:
>
>> cnMissingValFillColor:
>>
>> ...
>> Also note that the triangular mesh contouring algorithm does not
>> distinguish between missing value areas and areas outside the grid
>> boundary. Therefore if *ContourPlot*
>> <http://ncl.ucar.edu/Document/HLUs/Classes/ContourPlot.shtml> is given
>> non-rectangular data or *trGridType*
>> <http://ncl.ucar.edu/Document/Graphics/Resources/tr.shtml#trGridType> is
>> explicitly set to TriangularMesh, the color index used will be the
>> larger value of those assigned to the resources *cnMissingValFillColor*
>> <http://ncl.ucar.edu/Document/Graphics/Resources/cn.shtml#cnMissingValFillColor>
>> and *cnGridBoundFillColor*
>> <http://ncl.ucar.edu/Document/Graphics/Resources/cn.shtml#cnGridBoundFillColor>.
>>
>>
>> Maybe Mary, Dave or Rick can say somthing more about it.
>>
>> -Karin
>>
>> Am 29.09.17 um 17:23 schrieb Guido Cioni:
>>
>> Yep, and I still get the same behaviour :(
>>
>> I also thought that was the case but then I read that "Transparent" is
>> the default option for cnMissingValFillColor.
>>
>> Maybe it has something to do with the unstructured grid that I'm using?
>>
>> On 29. Sep 2017, at 17:14, Karin Meier-Fleischer <meier-fleischer at dkrz.de>
>> wrote:
>>
>> Hi Guido, :-)
>>
>> have you tried the cnMissingValFillColor resource to set the color for
>> missing value?
>>
>>   ResC at cnFillPalette         = cmap_r
>>   ResC at cnMissingValFillColor = 0
>>
>> Bye,
>> Karin
>>
>> Am 29.09.17 um 16:55 schrieb Guido Cioni:
>>
>> Hi,
>> I'm trying to plot filled contour of wind speed overlaid on a map. In
>> order to mask small values of winds I've both masked the original data and
>> set the first color of the color palette as transparent, i.e.
>>
>> cmap_r=read_colormap_file("wind_17lev")
>> cmap_r(0,3)=0.0
>> ResC at cnFillPalette= cmap_r
>>
>> However, when drawing with ResC at cnFillMode = "RasterFill", this causes
>> the Missing Values to be coloured with white instead that being
>> transparent, as you can see in the attached picture.
>>
>>
>>
>> Going back to old discussion this seems to be an old problem that was
>> fixed in 6.2.0. Am I wrong?
>>
>> I'm attaching the script that I'm using, although it is not 100% clean.
>> Cheers
>>
>>
>>
>> Guido Cioni
>> http://guidocioni.altervista.org
>>
>>
>>
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>> Guido Cioni
>> http://guidocioni.altervista.org
>>
>>
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>
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