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Ferret "how to": polar stereographic projections
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
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