Ferret "how to": polar stereographic projections

[hankin@xxxxxxxxxxxxxxxxxxx (Steve Hankin)]

Ferret how-to:  making polar stereographic plots

On Sep 28,  9:05am, Fenglin Yin wrote:
    > Subject: Please help on polar projection
    > Hi Steve,
    >
    > It is Yin again who needs your help.  I am trying
    > to do a contour on a polar projection:
    >
    > yes? set data coads_climatology
    > yes? go polar_2d fill/l=1/y=60:90 sst	! "70" -> "60" *sh* ed.
    >  **ERROR: invalid command: Sampling of SST[T=01-JAN00:45:31-DEC06:34,D=1]
	 is ambiguous on T axis
    > ...
    > It does not seem to work.
    >
    > On the other hand, the demo "go polar_demo"
    > works perfect.  I think I misundertand something here.
    > Do I need to do something extra to do a plot on a polar
    > projectin, instead of simply "go polar_2d" ?
    >
    > Many thanks.

=====================================================================

Hi Yin,

Your confusion is understandable.  There are two coordinate systems involved
in a Ferret projected plot -- one is the coordinate system of the variable,
itself (latitudes and longitudes); the other is the coordinate system of the
plotted page (set to be x=-1:1 and y=1-:1 in abstract page location units).

When you pass "FILL/l=1/y=60:90" as an argument to "go polar_2d" the FILL
command refers to the coordinate system of the page so the qualifiers ("/l="
and "/y=") are not being applied to the variable.  Here is the way to obtain
your results (parentheses indicate optional commands):

(yes? set window/asp=1:ax		! square)
(yes? go/help polar_2d			! check out the argument list ...)
yes? let my_sst = sst[l=1,y=60:90]	! region applied to "sst" directly
yes? go polar_2d fill my_sst 0 201 .3
(yes? show grid polar[d=polar_grid.dat]	! to help understand ...)
(yes? go polar_land)
(yes? go polar_grid)

! to see the same data in a rectangular plot ...
yes? set window/new/asp=.5
yes? go graticule
yes? fill my_sst
yes? go land
yes? go tics	! restore normal tics

... of course you may find there's a dissappointing lack of COADS data up
there.

	- steve




--

		|  NOAA/PMEL               |  ph. (206) 526-6080
Steve Hankin	|  7600 Sand Point Way NE  |  FAX (206) 526-6744
		|  Seattle, WA 98115-0070  |  hankin@pmel.noaa.gov


--- End of forwarded mail from hankin@rogue.pmel.noaa.gov (Steve Hankin)


-- 

		|  NOAA/PMEL               |  ph. (206) 526-6080  
Steve Hankin	|  7600 Sand Point Way NE  |  FAX (206) 526-6744
		|  Seattle, WA 98115-0070  |  hankin@pmel.noaa.gov