[ncl-talk] gsn_contour_map, zoom in plot problem

[Mary Haley]

I think the issue is that "o3_p", which is the variable you are trying to
plot, doesn't have any metadata attached to it.

When you do calculations like this in NCL:

   o3= a->O3(3,4,:,:) ; 18GTM = 11AM PST

  printVarSummary(o3)
   o3_p =(o3*1e9)*(28.97/48)

The "o3" will have metadata because no computations were done when you read
the variable off the file.

However, since o3_p involves calculations, NCL will strip all the metadata
and the only thing that o3_p will retain from o3 is the _FillValue
attribute, if any.

As a "trick", you can force o3_p to have the same metadata by doing the
following:

   o3_p = a->O3(3,4,:,:) ; 18GTM = 11AM PST

   o3_p =(o3_p*1e9)*(28.97/48)

The first line will read the data into o3_p, and the metadata will all be
there. Then, when you do the calculation, since o3_p already exists, no
metadata will be removed.

Note that I removed the use of o3, just to save memory. If you need to keep
o3 and o3_p around, then you can do:

   o3 = a->O3(3,4,:,:) ; 18GTM = 11AM PST
   o3_p = o3           ; trick to copy metadata
   o3_p =(o3*1e9)*(28.97/48)

You should however, update the long_name and units attributes of o3_p, to
reflect what the new values represent.

--Mary


On Wed, Sep 6, 2017 at 5:05 PM, Ying Song <ying.song at sjsu.edu> wrote:

> Hello, ncl helper,
>
> I trying to plot MERRA-2 reanalysis data in NCL using gsn_contour_map. I
> am only interested in west coast of US.  But I can not get the zoom in plot
> correctly by using resources:
>
>   res at mpMinLatF               = 30
>   res at mpMaxLatF               = 45
>   res at mpMinLonF               = -130
>   res at mpMaxLonF               = -110
>
> The warning shows:
> warning:ContourPlotDraw: out of range coordinates encountered; standard
> AreaFill rendering method may be unreliable;
>  consider setting the resource trGridType to "TriangularMesh" if
> coordinates contain missing values
>
> Attachment is my script. The info of MERRA-2 O3 data from printVarSummary
> is:
>  ------------------------------
> Variable: o3
> Type: float
> Total Size: 279465984 bytes
>             69866496 values
> Number of Dimensions: 4
> Dimensions and sizes:   [time | 8] x [lev | 42] x [lat | 361] x [lon | 576]
> Coordinates:
>             time: [0..1260]
>             lev: [1000..0.1000000014901161]
>             lat: [ -90..  90]
>             lon: [-180..179.375]
> Number Of Attributes: 11
>   long_name :   ozone_mass_mixing_ratio
>   units :       kg kg-1
>   _FillValue :  1e+15
>   missing_value :       1e+15
>   fmissing_value :      1e+15
>   scale_factor :         1
>   add_offset :   0
>   standard_name :       ozone_mass_mixing_ratio
>   vmax :        1e+15
>   vmin :        -1e+15
>   valid_range : ( -1e+15, 1e+15 )
> ---------------------------------------------------------
>
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