[ncl-talk] An issue with shaded contours in NCL6.4.0

[Saji Hameed]

Dear NCL developers,

I would like to report a rather strange issue that appears in version 6.4.0
of NCL.
The issue is related to shaded contours. For me, the issue happens when
using a dataset for which a mask was applied to "undefine" values over a
portion of the
domain.

I have attached four figures to illustrate the issue (two of these were
made with
NCL version 6.3.0, and the other two with NCL 6.4.0).

nomask_ncl6.4.png and nomask_ncl6.3.png are plots of rainfall made using
NCL 6.4.0 and NCL 6.3.0 respectively. There are two panels, with the top
showing a shaded contour plot, and the bottom a simple contour plot.
In the cases shown above, all data in the domain were used. There are no
issues with both the above mentioned plots (they are also identical to each
other, as expected).

In the next set of plots, I have masked the data over land areas. Once I do
this, I get
unexpected colors (white) for some contour levels (between 10 and 12) only
when using NCL6.4.0.
There is no issue with NCL6.3.0, which plots the data without any apparent
problems.

I did note this issue with other plots, but at that time I thought that I
was overusing colors on my desktop, and my OS could not allocate enough
colors to NCL. But only today, I figured out that this is seemingly related
to use of a mask to undefine
portions of the data domain.

For the time being, I will use NCL6.3.0, and hope that the source of this
issue
can be found and fixed.

Best regards,
saji
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