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interpolation bug?

Added by Jay Su over 7 years ago

Hi CDO team,

when we use

cdo interpolation,mygrid ifile ofile

when interpolation = remapdis, remapnn, or remaplaf
and the ifile is only defined in a region but mygrid is on the globe,
there will be funny pixel values in ofile outside the initial region.

Our CDO version is 1.6.9 and we saw "Remapping bug for non global grids [Bug #7625]" in the 1.8.1 release note. Are we talking about the same thing?

Thanks,
Jay


Replies (13)

RE: interpolation bug? - Added by Ralf Mueller over 7 years ago

I dont think so. For example remapdis uses a search radius of 180 degrees. Hence, if you only have regional data, the rest of the globe will look awkward. If you want something more realistic, use remapcon.

cheers
ralf

RE: interpolation bug? - Added by Jay Su over 7 years ago

Thank you Ralf.

How about remapnn and remaplaf?

RE: interpolation bug? - Added by Ralf Mueller over 7 years ago

remapnn works in the same way, you will get "artefacts" from the the other side of the globe. remaplaf creates artefacts in N-S-direction. For avoiding this, you should use remapcon.

hth
ralf

RE: interpolation bug? - Added by Uwe Schulzweida over 7 years ago

You can switch off the extrapolation by setting the environment variable

REMAP_EXTRAPOLATE=off

RE: interpolation bug? - Added by Uwe Schulzweida over 7 years ago

The values outside the initial region created with remaplaf are wrong. This bug will be fixed in the next CDO release. Thanks for the report!

RE: interpolation bug? - Added by Ralf Mueller over 7 years ago

Uwe Schulzweida wrote:

You can switch off the extrapolation by setting the environment variable
[...]

..... I should have know that ;-)

RE: interpolation bug? - Added by Jay Su over 7 years ago

Thank you Uwe.

RE: interpolation bug? - Added by Jay Su over 7 years ago

Hi Uwe and Ralf,

I tried

export REMAP_EXTRAPOLATE=off

then run the cdo code. But I did not see the change. Could you tell me what to do next?

Thanks,
Jay

RE: interpolation bug? - Added by Ralf Mueller over 7 years ago

Are you still using 1.6.9?

RE: interpolation bug? - Added by Jay Su over 7 years ago

Yes.

It takes long time for my IT dept to update the server.

RE: interpolation bug? - Added by Ralf Mueller over 7 years ago

With Anaconda, you can do it yourself without bothering your admins.

RE: interpolation bug? - Added by Jay Su over 7 years ago

REMAP_EXTRAPOLATE=off does not work with 1.6.9?

No write permissions with conda ...

RE: interpolation bug? - Added by Ralf Mueller over 7 years ago

Jay Su wrote:

REMAP_EXTRAPOLATE=off does not work with 1.6.9?

Could be that it was introduced in a later version

No write permissions with conda ...

default is to install it into your home directory - so you should not have permission problems.

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