Re: structure of geo_borders.cdf

[Steve Hankin <hankin@xxxxxxxxxxxxx>]

Hi Martin,

These commands reveal the trick:

     yes? use geo_borders
     yes? stat/brief CONTINENT_LON
      Total # of data points: 22585 (22585*1*1*1)
      # flagged as bad  data: 1752
      Minimum value: -180
      Maximum value: 739.92
      Mean    value: 286.63 (unweighted average)

Note the longitude range: -180:740.  The values are actually replicated:
in -180:180, repeated again 180:540 and yet again for another
hemisphere. (-180 to 540 would be sufficient for nearly all cases.)

To illustrate, note for example that this works fine

     yes? go basemap x=180:540
     yes? go land

whereas here you'll see the upper bound of the longitudes

     yes? go basemap x=540:900
     yes? go land

If you issue the command "yes? ppl list xaxis" after the final example
just above you'll see that the PLOT+ graphics in Ferret sees an X range
of 540:900.  The points which lie outside of this range are simply
clipped. Clipped points have only minor impact on performance.

    - steve

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

Martin Schmidt wrote:

> Hi all,
>
> I am trying to generate regional high resolution land masks,
> which do basically the same as 'go land'. The main task is to
> generate a file with the same structure like geo_borders.cdf. I
> get problems, when the Greenwich meridian is crossed. If
> longitudes west of the Greenwich meridian are counted as
> negative in both, the displayed variables and the coordinats of
> land contours in my regional version of geo_borders.cdf
> everything works fine. Also if longitudes are counted from, say
> 350 to 370 degrees, I get correct plots. However, drawing a
> variable with negative western longitudes, land contors defined
> from 350 to 370 degrees are not shown. The original "go land"
> works!
>
> Is anyone able to explaine the following
>
> use coads_climatology
> shade/l=1/x=-5:15/y=54:60 sst
> go land
>
> works.
>
> shade/l=1/x=0:20 sst
> go land

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