[ncl-talk] Regridding from OSGB spatial coordinate to Latitude-longitude in rotated pole coordinates

Thu Feb 25 10:45:40 MST 2021

Hi Dennis,
The data draws on a wrong location and the map boundary is not aligning.
It should plot over the UK which is about 50-60N.

Thanks.

On Thu, Feb 25, 2021 at 5:41 PM Dennis Shea <shea at ucar.edu> wrote:

> It helps to give NCL the correct lat/lon array information.
>
> See attached
>
> On Thu, Feb 25, 2021 at 10:23 AM Dave Allured - NOAA Affiliate via
> ncl-talk <ncl-talk at mailman.ucar.edu> wrote:
>
>> That script looks pretty good.  You can see from the error messages that
>> NCL is trying to understand @lat2d and @lon2d, but something is not quite
>> right with them.  We need to see printVarSummary for tas, tas at lat2d, and
>> tas at lon2d.  It is possible that dimensions are mismatched between data
>> and coordinates, for some reason.
>>
>> There is also this note in that doc page:  "If your data variable is a
>> two-dimensional (2D) array ordered lon x lat, you will need to reorder it
>> to be lat x lon."  Please check and see if this is the problem.
>>
>>
>> On Thu, Feb 25, 2021 at 10:00 AM S Br <sbr.climate at gmail.com> wrote:
>>
>>>
>>> Hi Dave,
>>> Many thanks for your reply. Sorry I missed to provide the details.
>>> I have run the following NCL script  and came across the errors given
>>> below.
>>> You can see the attached plot that it draws value throughout the globe.
>>> It is supposed to be drawn only over the UK.
>>> Am I doing something wrong?
>>>
>>> ;********
>>> srcFileName="tas_rcp85_land-rcm_uk_12km_01_mon_198012-208011.nc"
>>>
>>> ;---Read File
>>> f=addfile(srcFileName,"r")
>>> print(f)
>>>
>>> ;---Get the source lat/lon grid
>>> tas=f->tas(0,0,:,:)
>>> tas at lat2d=f->projection_y_coordinate
>>> tas at lon2d=f->projection_x_coordinate
>>>
>>> ;---Plot data
>>>   wks = gsn_open_wks("x11","map")
>>>
>>>   res              = True
>>>   res at gsnMaximize  = True     ; maximize plot in frame
>>>   res at cnFillOn     = True     ; turn on contour fill
>>>   res at cnLinesOn    = False    ; turn off contour fill
>>>   res at gsnAddCyclic     = False
>>> ;   res at mpMinLatF    =  48.0             ; only plot 30S to 30N
>>> ;   res at mpMaxLatF    =  60.0
>>> ;  res at mpMinLonF    =  -15.0          ; only plot 30S to 30N
>>> ;   res at mpMaxLonF    = 6.0
>>>  res at mpDataBaseVersion = "MediumRes"
>>>    res at mpLandFillColor = "white"
>>>
>>>   plot = gsn_csm_contour_map(wks,tas(:,:),res)
>>>
>>> ********************
>>> (0) is_valid_latlon2d_attr: Warning: The 'lat2d' attribute must either be
>>> (0) the same dimension sizes as the data, or one element larger in both
>>> directions.
>>> (0) Your data will most likely not be overlaid on the map correctly.
>>> (0) check_for_y_lat_coord: Warning: Data either does not contain
>>> (0) a valid latitude coordinate array or doesn't contain one at all.
>>> (0) A valid latitude coordinate array should have a 'units'
>>> (0) attribute equal to one of the following values:
>>> (0)    'degrees_north' 'degrees-north' 'degree_north' 'degrees north'
>>> 'degrees_N' 'Degrees_north' 'degree_N' 'degreeN' 'degreesN' 'deg north'
>>> (0) is_valid_latlon2d_attr: Warning: The 'lon2d' attribute must either be
>>> (0) the same dimension sizes as the data, or one element larger in both
>>> directions.
>>> (0) Your data will most likely not be overlaid on the map correctly.
>>> (0) check_for_lon_coord: Warning: Data either does not contain
>>> (0) a valid longitude coordinate array or doesn't contain one at all.
>>> (0) A valid longitude coordinate array should have a 'units'
>>> (0) attribute equal to one of the following values:
>>> (0)    'degrees_east' 'degrees-east' 'degree_east' 'degrees east'
>>> 'degrees_E' 'Degrees_east' 'degree_E' 'degreeE' 'degreesE' 'deg east'
>>>
>>> On Thu, Feb 25, 2021 at 4:17 PM Dave Allured - NOAA Affiliate <
>>> dave.allured at noaa.gov> wrote:
>>>
>>>> Does your file contain its own lat and lon coordinate arrays?  You will
>>>> need to check this yourself with ncdump or NCL plus print commands.
>>>>
>>>> If the file has its own coordinate arrays, then do not regrid or
>>>> reproject.  Doing that will lose detail and reduce the quality of the
>>>> plotted image.  NCL is quite capable of directly displaying any data with
>>>> attached coordinate arrays, and it does not need to know anything about the
>>>> projection of the data.  Please see documentation for "Plotting data on a
>>>> map" for much more information about aligning data on a map plot.
>>>>
>>>>     https://www.ncl.ucar.edu/Applications/plot_data_on_map.shtml
>>>>
>>>> If the coordinate arrays in the file are two dimensional, then see
>>>> example 3, "Curvilinear grid".  When you have 2-D coordinates, they must be
>>>> passed to the NCL plot routine with special attributes *lat2d* and
>>>> *lon2d*, or alternatively *sfXArray* and *sfYArray* attached to the
>>>> plot resource variable.  Note that 1-D coordinates do not need this special
>>>> treatment because they are normally attached directly to the data variable
>>>> to plot.
>>>>
>>>>
>>>> On Thu, Feb 25, 2021 at 8:24 AM S Br via ncl-talk <
>>>> ncl-talk at mailman.ucar.edu> wrote:
>>>>
>>>>> Hi All,
>>>>> I have a set of regional gridded data in the British National Grid
>>>>> (OSGB) spatial coordinate system. I am looking to use this data in NCL but
>>>>> the projection is not correctly displayed? Could it be possible to regrid
>>>>> this data to Latitude-longitude in rotated pole coordinates or to a regular
>>>>> lat/lon grid.
>>>>>
>>>>> I would like to mention that these data sets are generated using the
>>>>> Iris package in Python. The data is correctly displayed in Python but not
>>>>> in NCL.
>>>>>
>>>>> For your convenience I have attached here a sample NetCDF file.
>>>>>
>>>>> Thank you.
>>>>> SBR
>>>>>
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