[ncl-talk] joint-histogram

Mary Haley haley at ucar.edu
Tue Nov 14 10:05:50 MST 2017 

Hi Marston,

The reason you are seeing what looks like log values is because the Y
coordinate array is irregularly spaced, and NCL by default will take your
irregular Y axis values and place them linearly on the Y axis.

I don't know if this is intentional, but you have:

  im!0 ="x"
  im!1 ="y"

Dimension 0 is associated with the Y axis, and dimension 1 is the X axis.
Just wanted to point that out, since you are calling dimension 0 "x", and
dimension 1 "y".  I changed this to:

  im!1 ="x"
  im!0 ="y"

Which seems to make your plot match better with the one you attached.
You can't make x a coordinate array, because it has one more element than
the X dimension of your data.

Instead, in order to associate the x and y values with your plot, use these
special resources, which are mentioned in the raster_5.ncl example on the
same page:

res at sfXArray             = x
res at sfYArray             = y

Finally, you are going to get weird labels on your axes, because NCL is
simply trying to put labels along the X axis where it thinks it makes
sense. If you want the same labels on your axes as your actual x values,
then set:

res at tmXBMode             = "Explicit"
res at tmXBValues           = x
res at tmXBLabels           = ""+x    ; labels have to be strings

See attached.

--Mary





On Mon, Nov 13, 2017 at 6:04 PM, Marston Johnston <shejo284 at gmail.com>
wrote:

> Hi Mary,
>
> Thanks for the tips in the table. However, there is a better example:
>
> https://www.ncl.ucar.edu/Applications/raster.shtml
>
> However, I’m having some trouble with the finer details of the plot. It
> involves getting the tick labels just in the correct place.
>
> My code below is basically example 6, which looks very much like the same
> coordinate values of one of the iSCCP products:
>
> I’m trying to compare my model output with the above figure but there are some issue:
>
> 1.) In the ncl example 6, the figure dimension is 7x6 while mine is 7x7. When I plot it as below I get log x-axis despite my values not being log.
>
> 2.) None of the labels ended up on the major axis.
>
> I’m not sure how NCL axis works. Could I get some tips on how to force the axis to fall on the grid edges as in the figure above?
>
>   im =
>    (/(/0.60   0.81   1.86   3.83   3.09   0.78   0.01/), (/0.45   0.63   1.47   4.96   5.45   2.27   0.28/), \ (/0.60   0.66   0.88   2.03   2.45   1.56   0.50/),(/0.76   0.91   1.02   1.17   1.46   1.44   0.63/), \
>
>    (/0.85   1.41   1.32   0.88   0.91   1.07   0.72/),(/1.55   1.84   1.24   0.70   0.41   0.46   0.36/), (/7.19   1.73   0.60   0.28   0.14   0.08   0.05/)/)
>
> x = (/0.0,0.3,1.3,3.6,9.4,23.0,60.0,100.0/)
> y = (/1000.0,800.0,680.0,560.0,440.0,310.0,180.0/)
>
> im!0=“x"
> im!1 =“y”
> im&x = x
> im&y = y
>
> wks  = gsn_open_wks("png","raster")      ; send graphics to PNG file
> res                      = True          ; plot mods desired
> res at cnFillOn             = True          ; Turn on contour fill
> res at cnFillMode           = "RasterFill"  ; Turn on raster fill
> res at cnLinesOn            = False        ; Turn off contour lines
> res at cnLineLabelsOn       = False         ; turns off contour line labels
> res at cnFillPalette        = "BlAqGrYeOrReVi200";MPL_viridis"
> res at lbLabelBarOn         = True
> res at lbOrientation        = "vertical"     ; vertical label bar
>
> plot = gsn_csm_contour(wks,im,res)       ; contour the variable
>
> Best,
> /M
>
> *Marston S. Ward*
>
> On 16 Oct 2017, 21:31 +0200, Mary Haley <haley at ucar.edu>, wrote:
>
> Marston,
>
> Take a look at this page:
>
> http://www.ncl.ucar.edu/Applications/table.shtml
>
> These are examples showing how to draw filed cells (square or triangle)
> based on some criteria.  I think table_4.ncl colors the cells by ranges of
> values.
>
> --Mary
>
>
> On Mon, Oct 16, 2017 at 1:03 PM, Marston Johnston <shejo284 at gmail.com>
> wrote:
>
>> Hi Dennis,
>>
>>
>>
>> At first glance it would appear so, but example 6 calculates the
>> percentage. In the ucar example:
>>
>> https://climatedataguide.ucar.edu/climate-data/isccp-interna
>> tional-satellite-cloud-climatology-project
>>
>>
>>
>> The ISCCP cloud fraction is calculated for each bin instead of density of
>> the frequency of occurrence. So in example 6 there are 2 datasets that are
>> used as input data, but in the figure in question seems to use 3.
>>
>>
>>
>> /M
>>
>>
>>
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>
>> Marston S. Ward, PhD
>>
>> Department of Earth Sciences
>>
>> University of Gothenburg, Sweden
>>
>> Email: marston.johnston at gu.se
>>
>> SkypeID: marston.johnston
>>
>> Phone: +46-31-7864901 <+46%2031%20786%2049%2001>
>>
>> Only the fruitful thing is true!
>>
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>
>>
>>
>>
>>
>> *From:* ncl-talk <ncl-talk-bounces at ucar.edu> on behalf of Dennis Shea <
>> shea at ucar.edu>
>> *Date:* Monday, 16 October 2017 at 20:53
>> *To:* Marston Ward <marston.johnston at gu.se>
>> *Cc:* "ncl-talk at ucar.edu" <ncl-talk at ucar.edu>
>> *Subject:* Re: [ncl-talk] joint-histogram
>>
>>
>>
>> I am not a graphics person.
>>
>> Looks like example 6
>> https://www.ncl.ucar.edu/Applications/pdf.shtml
>>
>> ===
>>
>> Really, a contour plot with raster mode.
>>
>>
>>
>> On Mon, Oct 16, 2017 at 12:46 PM, Marston Ward <marston.johnston at gu.se>
>> wrote:
>>
>> Hi guys!
>>
>>
>>
>> I’m trying to develop a NCL script to produce the attached figure, which
>> is a joint-histogram, but a bit different from what pdfxy produces.
>>
>> I have a good idea of how this image is produced; but why reinvent the
>> wheel? I don’t think that NCL has such a plot function, or am I mistaken?
>>
>> Does anyone have such a script – and would like to share?
>>
>> This is something I can definitely think of contributing to the NCL.
>>
>>
>>
>> Best,
>>
>> /M
>>
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>
>> Marston S. Ward, PhD
>>
>> Department of Earth Sciences
>>
>> University of Gothenburg, Sweden
>>
>> Email: marston.johnston at gu.se
>>
>> SkypeID: marston.johnston
>>
>> Phone: +46-31-7864901 <+46%2031%20786%2049%2001>
>>
>> Only the fruitful thing is true!
>>
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>
>>
>>
>>
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