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Re: [ferret_users] Interpolation on co-range chart



Hi Dan,

For regular grids, the data should be on a modulo axis in longitude. Then interpolation should also work in the right way as the axis is correctly "wrapped" around the globe.
<http://ferret.pmel.noaa.gov/Ferret/documentation/users-guide/Grids-Regions/REGIONS#Chapter4-Modulo_axes>

When I had the same problem with single irregularly spaced data points, I created a new variable shifted by 180 degrees in longitude. Then, before interpolating, I tested the range longitudes and when it was close to 360°/0°, then I interpolated on the new shifted variable instead and subsequently shifted the result back by 180 degrees. That was the easiest way for me to use the internal "set mode interpolate" when dealing with single longitude values.

Cheers,
Hella



------------------------------------------------------------------------
*Subject:* [ferret_users] Interpolation on co-range chart
*Sent:* 2010-10-14 12:15:54 +0800
*From:* Yu, Hao-Cheng <danish.url@xxxxxxxxx>
*To:* ferret_users@xxxxxxxx

Dear ferret users,

I try to plot co-range chart with global tide data.
I notice ferret interpolated the values when the degree values across 360
(or 0).
For example, the region between 5 and 355, ferret will interpolate to 180.
(Should be 0)
This will cause lots of contour line in this region, and give wrong
interpolation values.
Is there anyone do such interpolation and avoid error like this?


Sincerely, dan


--

---------------------------------------------------------------
 Hella Riede  (Dipl.Chem.)
 Max Planck Institute for Chemistry
 Dept. of Atmospheric Chemistry
 Becherweg 27                   email: hella.riede@xxxxxxx
 55128 Mainz                    phone: +49-6131-305437
 Germany                        fax:   +49-6131-305436

 homepage: www.mpch-mainz.mpg.de/~riede
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