[ncl-talk] Regridding from OSGB spatial coordinate to Latitude-longitude in rotated pole coordinates
Dave Allured - NOAA Affiliate
dave.allured at noaa.gov
Fri Feb 26 09:38:19 MST 2021
Progress. This proves that arrays grid_latitude and grid_longitude are
wrong in the input file. This is no longer an NCL problem, except for
possibly trying to reproject the data using projection parameters. I think
Dennis already said this projection is not supported in NCL, so that would
be difficult.
I recommend asking Iris support for help to generate the correct lat and
lon arrays. You can show them the invalid coordinates directly, leaving
NCL out of the loop, by sampling the output from:
ncdump -v grid_latitude,grid_longitude file.nc
It may also be possible to get the correct coordinate arrays by some other
method. You might ask the original data provider if they can supply the
correct lat and lon arrays to match their data. If you can get corrected
arrays, it would be easy to retrofit them into your temperature data file.
On Fri, Feb 26, 2021 at 2:34 AM S Br <sbr.climate at gmail.com> wrote:
> Hi,
> The min and max of f->grid_latitude and f->grid_longitude prints wrong
> information. You can see that the bounding box is not surrounding the UK.
>
> (0) min=-0.8710618968191547 max=12.94984143216418
> (0) min=-18.24145632530888 max=-6.580251255557555
>
> Thanks.
>
> On Thu, Feb 25, 2021 at 9:24 PM Dave Allured - NOAA Affiliate <
> dave.allured at noaa.gov> wrote:
>
>> Okay. We need to evaluate whether the lat and lon coordinates in your
>> file are correct. I see Dennis's other reply, but I am suggesting a
>> different approach using only attached coordinates, and nothing else. If
>> the Iris package generated your file correctly, then nothing else should be
>> needed.
>>
>> Please show the min and max of f->grid_latitude and f->grid_longitude.
>> Don't show the whole array. The command *printMinMax (var, 0)* is
>> useful for this. If these coordinate sets are correct, then the min and
>> max should be a bounding box surrounding the UK.
>>
>> NCL works best with supplied coordinate arrays, which is the method I am
>> recommending here. Python is doing something different, perhaps
>> recalculating based on the projection information. I don't really care
>> about that, I just want to help you get the normal NCL method working.
>>
>>
>> On Thu, Feb 25, 2021 at 1:20 PM S Br <sbr.climate at gmail.com> wrote:
>>
>>> Hi Dave,
>>> Please see the attached plot, this is how it looks like if we use the
>>> above statements.
>>> It obviously doesn't plot over the UK.
>>>
>>>
>>> On Thu, Feb 25, 2021 at 6:59 PM Dave Allured - NOAA Affiliate <
>>> dave.allured at noaa.gov> wrote:
>>>
>>>> I see what's going on. From your other e-mail, the data file contains
>>>> two different sets of coordinates. There are the projection coordinates in
>>>> meters. Those are not latitudes and longitudes, therefore not sufficient
>>>> for NCL. But the geographic coordinates are also provided. Double
>>>> coordinates are frequently encountered in GIS related applications. Try
>>>> this:
>>>>
>>>> tas at lat2d=f->grid_latitude
>>>> tas at lon2d=f->grid_longitude
>>>>
>>>>
>>>> On Thu, Feb 25, 2021 at 11:42 AM S Br <sbr.climate at gmail.com> wrote:
>>>>
>>>>> If I print tas at lat2d and tas at lon2d, they give the following
>>>>> information.
>>>>>
>>>>> Variable: taslat
>>>>> Type: double
>>>>> Total Size: 896 bytes
>>>>> 112 values
>>>>> Number of Dimensions: 1
>>>>> Dimensions and sizes: [112]
>>>>> Coordinates:
>>>>> (0) -102000
>>>>> (1) -90000
>>>>> (2) -78000
>>>>> (3) -66000
>>>>> (4) -54000
>>>>> (5) -42000
>>>>> (6) -30000
>>>>> (7) -18000
>>>>> (8) -6000
>>>>> (9) 6000
>>>>> (10) 18000
>>>>> (11) 30000
>>>>> (12) 42000
>>>>> (13) 54000
>>>>> (14) 66000
>>>>> (15) 78000
>>>>> (16) 90000
>>>>> (17) 102000
>>>>> (18) 114000
>>>>> (19) 126000
>>>>> (20) 138000
>>>>> (21) 150000
>>>>> (22) 162000
>>>>> (23) 174000
>>>>> (24) 186000
>>>>> (25) 198000
>>>>> (26) 210000
>>>>> (27) 222000
>>>>> (28) 234000
>>>>> (29) 246000
>>>>> (30) 258000
>>>>> (31) 270000
>>>>> (32) 282000
>>>>> (33) 294000
>>>>> (34) 306000
>>>>> (35) 318000
>>>>> (36) 330000
>>>>> (37) 342000
>>>>> (38) 354000
>>>>> (39) 366000
>>>>> (40) 378000
>>>>> (41) 390000
>>>>> (42) 402000
>>>>> (43) 414000
>>>>> (44) 426000
>>>>> (45) 438000
>>>>> (46) 450000
>>>>> (47) 462000
>>>>> (48) 474000
>>>>> (49) 486000
>>>>> (50) 498000
>>>>> (51) 510000
>>>>> (52) 522000
>>>>> (53) 534000
>>>>> (54) 546000
>>>>> (55) 558000
>>>>> (56) 570000
>>>>> (57) 582000
>>>>> (58) 594000
>>>>> (59) 606000
>>>>> (60) 618000
>>>>> (61) 630000
>>>>> (62) 642000
>>>>> (63) 654000
>>>>> (64) 666000
>>>>> (65) 678000
>>>>> (66) 690000
>>>>> (67) 702000
>>>>> (68) 714000
>>>>> (69) 726000
>>>>> (70) 738000
>>>>> (71) 750000
>>>>> (72) 762000
>>>>> (73) 774000
>>>>> (74) 786000
>>>>> (75) 798000
>>>>> (76) 810000
>>>>> (77) 822000
>>>>> (78) 834000
>>>>> (79) 846000
>>>>> (80) 858000
>>>>> (81) 870000
>>>>> (82) 882000
>>>>> (83) 894000
>>>>> (84) 906000
>>>>> (85) 918000
>>>>> (86) 930000
>>>>> (87) 942000
>>>>> (88) 954000
>>>>> (89) 966000
>>>>> (90) 978000
>>>>> (91) 990000
>>>>> (92) 1002000
>>>>> (93) 1014000
>>>>> (94) 1026000
>>>>> (95) 1038000
>>>>> (96) 1050000
>>>>> (97) 1062000
>>>>> (98) 1074000
>>>>> (99) 1086000
>>>>> (100) 1098000
>>>>> (101) 1110000
>>>>> (102) 1122000
>>>>> (103) 1134000
>>>>> (104) 1146000
>>>>> (105) 1158000
>>>>> (106) 1170000
>>>>> (107) 1182000
>>>>> (108) 1194000
>>>>> (109) 1206000
>>>>> (110) 1218000
>>>>> (111) 1230000
>>>>>
>>>>>
>>>>> Variable: taslon
>>>>> Type: double
>>>>> Total Size: 656 bytes
>>>>> 82 values
>>>>> Number of Dimensions: 1
>>>>> Dimensions and sizes: [82]
>>>>> Coordinates:
>>>>> (0) -210000
>>>>> (1) -198000
>>>>> (2) -186000
>>>>> (3) -174000
>>>>> (4) -162000
>>>>> (5) -150000
>>>>> (6) -138000
>>>>> (7) -126000
>>>>> (8) -114000
>>>>> (9) -102000
>>>>> (10) -90000
>>>>> (11) -78000
>>>>> (12) -66000
>>>>> (13) -54000
>>>>> (14) -42000
>>>>> (15) -30000
>>>>> (16) -18000
>>>>> (17) -6000
>>>>> (18) 6000
>>>>> (19) 18000
>>>>> (20) 30000
>>>>> (21) 42000
>>>>> (22) 54000
>>>>> (23) 66000
>>>>> (24) 78000
>>>>> (25) 90000
>>>>> (26) 102000
>>>>> (27) 114000
>>>>> (28) 126000
>>>>> (29) 138000
>>>>> (30) 150000
>>>>> (31) 162000
>>>>> (32) 174000
>>>>> (33) 186000
>>>>> (34) 198000
>>>>> (35) 210000
>>>>> (36) 222000
>>>>> (37) 234000
>>>>> (38) 246000
>>>>> (39) 258000
>>>>> (40) 270000
>>>>> (41) 282000
>>>>> (42) 294000
>>>>> (43) 306000
>>>>> (44) 318000
>>>>> (45) 330000
>>>>> (46) 342000
>>>>> (47) 354000
>>>>> (48) 366000
>>>>> (49) 378000
>>>>> (50) 390000
>>>>> (51) 402000
>>>>> (52) 414000
>>>>> (53) 426000
>>>>> (54) 438000
>>>>> (55) 450000
>>>>> (56) 462000
>>>>> (57) 474000
>>>>> (58) 486000
>>>>> (59) 498000
>>>>> (60) 510000
>>>>> (61) 522000
>>>>> (62) 534000
>>>>> (63) 546000
>>>>> (64) 558000
>>>>> (65) 570000
>>>>> (66) 582000
>>>>> (67) 594000
>>>>> (68) 606000
>>>>> (69) 618000
>>>>> (70) 630000
>>>>> (71) 642000
>>>>> (72) 654000
>>>>> (73) 666000
>>>>> (74) 678000
>>>>> (75) 690000
>>>>> (76) 702000
>>>>> (77) 714000
>>>>> (78) 726000
>>>>> (79) 738000
>>>>> (80) 750000
>>>>> (81) 762000
>>>>>
>>>>> On Thu, Feb 25, 2021 at 6:26 PM Dave Allured - NOAA Affiliate <
>>>>> dave.allured at noaa.gov> wrote:
>>>>>
>>>>>> It is starting to look like there is an error in the attached
>>>>>> coordinates. What are the min and max values of tas at lat2d and
>>>>>> tas at lon2d?
>>>>>>
>>>>>>
>>>>>> On Thu, Feb 25, 2021 at 10:45 AM S Br <sbr.climate at gmail.com> wrote:
>>>>>>
>>>>>>> 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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