[ferret_users] Re: [ferret_users] Trying to visualize data on cubed-sphere grid

["Patrick Brockmann" <Patrick.Brockmann@xxxxxxxxxxxx>]

> Hi Patrick,
> About the polygon command, I believe that Ferret does fill in the 
> polygons that are defined. In the dataset Ki_cells.nc, I see cells where 
> the longitude values cross the branch cut. We would want to make some 
> correction, when we detect that this is what's happening. So for this cell,
> 
> yes? use Ki_cells
> yes? list/j=2171 bounds_lon
>               VARIABLE : BOUNDS_LON
>               FILENAME : Ki_cells.nc
>               SUBSET   : 6 points (X)
>               Y        : 2171
>             2171
>            2171
>   1   / 1:  174.5
>   2   / 2:  167.6
>   3   / 3:  172.1
>   4   / 4: -172.1
>   5   / 5: -167.6
>   6   / 6: -174.5
> 
> we should correct the longitudes.  What comes to my mind is an external 
> function, where we pass in the longitude vertex coordinates and a 
> tolerance for the size of jump that will mark the vertex locations for a 
> correction, and the return for a cell like this would be corrected, but 
> a cell such as
> 
>   1   / 1:   -5.5
>   2   / 2:  -12.4
>   3   / 3:   -7.9
>   4   / 4:    7.9
>   5   / 5:   12.4
>   6   / 6:    5.5
> 
> would not change.  Does that sound like a reasonable solution? It seems 
> to me that trying to put automated logic into the polygon plot code 
> itself might lead to results that wouldn't be well suited to all grids.

Hi Ansley,

You are right, this can be done by some conditionnal variables
but I wanted to avoid this kind of cooking to users.

Here is the code 
yes? use Ki_cells.nc
yes? set variable/units="degrees_east" BOUNDS_LON
yes? set variable/units="degrees_north" BOUNDS_LAT
yes? let bounds_lon1=if abs(bounds_lon-lon) lt 180 then bounds_lon else bounds_lon+360
yes? let bounds_lon2=if abs(bounds_lon1-lon) lt 180 then bounds_lon1 else bounds_lon-360
yes? yes? polygon/MODULO/COORD_AX=Y/line/fill/hlim=0:360 BOUNDS_LON2, BOUNDS_LAT, KI

Patrick
 
-- 
LSCE/IPSL, Laboratoire CEA-CNRS-UVSQ
Data Analysis and Visualization Engineer
ICMC - IPSL Climate Modelling Centre
--