[ncl-talk] Longitude Flip in ocean data

Mary Haley haley at ucar.edu
Fri Jan 15 13:43:23 MST 2016


Can you provide me with the data file so I can test this here?  It looks
like the longitude values should be flipping correctly, but I don't
understand why you are getting values from -257.75 to 101.75.

The longitude array must be monotonically increasing for this to work, I
believe, but I want to check the array myself to see what's going on with
it.

If your file is too large, then if you could just write sst to the file by
itself, and send me that, then I don't need anything else.

You can write sst to a file using the following code:


  system("rm marytest.nc")
  mout = addfile("marytest.nc","c")
  mout->sst = sst

You can upload the file to our ftp:

http://www.ncl.ucar.edu/report_bug.shtml#HowToFTP

or share it via Dropbox or Google Drive or something similar.

Thanks,

--Mary



On Wed, Jan 13, 2016 at 12:40 AM, Arun Kumar Dwivedi <
dwivedi.arunkumar at gmail.com> wrote:

> Dear all,
> Thank q for the response
> In continuation to my above query the description is given below
>
> Our data is rectilinear data ( data is in rectangular matrix with
> un-uniform spacing). '
>
> Our basic data structure is :
>
> Variable: sst
> Type: float
> Total Size: 4499840 bytes
>             1124960 values
> Number of Dimensions: 4
> Dimensions and sizes:    [T1 | 20] x [ZT_K1_1 | 1] x [YT_J | 178] x [XT_I
> | 316]
> Coordinates:
>             T1: [1005606..1005720]
>             ZT_K1_1: [ 2.5.. 2.5]
>             YT_J: [ -79..  79]
>             XT_I: [   1.. 359]
> Number Of Attributes: 4
>   missing_value :    -1e+34
>   _FillValue :    -1e+34
>   long_name :    SST
>   units :    C
>
>
> ****************************
> Our actual problem is we need to plot longitude in the selected range for
> eg -90W to 120E then it doesnt accept the -90W value since the longitude
> array is from 0 to 360 , the plot comes from 0 to 120E only. (-ve values
> not accepted.) . To solve this we used lonflip function so that our
> longitude array changes from -180 to 180. but since it is un-uniform data ,
> ***********************************
> After LonFlip , it is
>
> Variable: sstnew
> Type: float
> Total Size: 4499840 bytes
>             1124960 values
> Number of Dimensions: 4
> Dimensions and sizes:    [T1 | 20] x [ZT_K1_1 | 1] x [YT_J | 178] x [XT_I
> | 316]
> Coordinates:
>             T1: [1005606..1005720]
>             ZT_K1_1: [ 2.5.. 2.5]
>             YT_J: [ -79..  79]
>             XT_I: [-257.75..101.75]
> Number Of Attributes: 5
>   missing_value :    -1e+34
>   _FillValue :    -1e+34
>   long_name :    SST
>   units :    C
>   lonFlip :    longitude coordinate variable has been reordered via lonFlip
>
> The longitude is originally from 0 to 360 and after LonFlip it is
> -257.75..101.75... But when we are plotting in the longitude range (-90,
> 120) it is coming only in the longitude range (-90, 101)
>
> So what would be the solution for our problem
>
>
>
> Thanks & Regards
> Arun Kumar Dwivedi,
> Project Engineer - II
> Computational Earth Science Group
> CDAC, Pune - 411 007
> Mob :09546189035
>
> On Tue, Jan 12, 2016 at 7:44 PM, Mary Haley <haley at ucar.edu> wrote:
>
>> Arun,
>>
>> We need a little more information here.  Is your data on a rectilinear
>> grid? This function only works for rectilinear grids (grids represented by
>> 1D lat/lon arrays).
>>
>> Did you look at your longitude values to make sure there are no issues
>> with them before you do lonFlip?
>>
>> It would help if we could see a "printVarSummary" of the variable you are
>> trying to call lonFlip on, and also any error messages.
>>
>> --Mary
>>
>>
>> On Sun, Jan 10, 2016 at 11:10 PM, Arun Kumar Dwivedi <
>> dwivedi.arunkumar at gmail.com> wrote:
>>
>>> Dear All,
>>> I am working on ocean data (MOM and WAM) for global domain. I have
>>> issues with longitude, when trying to plot in for particular region. For eg
>>> if I want plot with Latitude 0 to 30 and Lon -40 to 100. Then it doesn't
>>> recognize the value -40 in the longitude array.
>>>
>>> For this i have tried using LonFlip function, it works fine with uniform
>>> grid but doesn't work with my data set which has varied grid resolution
>>> (0.5,1 and 1.5).
>>>
>>>
>>> Thanks & Regards
>>> Arun Kumar Dwivedi,
>>>
>>>
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>>>
>>>
>>
>
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