[ferret_users] Re: importance of "set grid var "command

[Ansley Manke <ansley.b.manke@xxxxxxxx>]

Hi -
In the northern hemisphere, or if you are not setting a subregion, then it often won't make a visible difference.  The default grid for Ferret operations is the abstract grid, that is XABSTRACT (x=1,2,3,...), YABSTRACT(y=1,2,3,...) and so on.  If we're in the Southern Hemisphere, then we want to refer to negative values of Y, and the script will fail with an error message.

Try this example, with the "set grid sst"  commented out:

  use coads_climatology
   go mp_stereographic_south
   ! set grid sst
   set region/x=0:360/y=-90:0/l=1
   go mp_aspect
  fill/nolab/nokey/noaxes sst, x_page, y_page

The definitions that are set up in the script mp_stereographic_south can't be applied to the abstract grid in the region /y=-90:0.  With the SET GRID SST, the grid is the grid of the variable sst which includes y==90:0

Ansley


jagadish karmacharya wrote:

Hi Ansley,

This is a very general question so i have not posted it to mailing list.
I am curious why we have to "set grid var"
before using "fill var"
can't we just issue "fill var" without issuing previous command, what's the  difference . I haven't noticed any difference in the plot
Regards
Jagadish
 
Ansley Manke <ansley.b.manke@noaa.gov> wrote:

Hi Martin,
It's a question of the order of operations. Put the "GO mp_grid" before
the go mp_aspect and the set region, and it'll work fine. (or use SET
GRID SST instead of mp_grid.jnl). mp_stereographic_south defines the
mapping variables based on pseudo-variables "X" and "Y". Until Ferret
knows what grid these are going to be coming from, it assumes they're
from the abstract axes X and Y, which hav e values X=1,2,3,... and
Y=1,2,3... So the region y=-90:0 can't be applied to that,. and the
error comes in mp_aspect which tries to use the mapping variables to set
up the window.

use coads_climatology
go mp_stereographic_south
go mp_grid sst
set region/x=0:360/y=-90:0/l=1
go mp_aspect
fill/nolab/nokey/noaxes sst, x_page, y_page

or

use coads_climatology
go mp_stereographic_south
set grid sst
set region/x=0:360/y=-90:0/l=1
go mp_aspect
fill/nolab/nokey/noaxes sst, x_page, y_page

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