[ncl-talk] Regridding from OSGB spatial coordinate to Latitude-longitude in rotated pole coordinates
Dennis Shea
shea at ucar.edu
Thu Feb 25 12:19:06 MST 2021
I **speculate** that the attributes associated with the
"transverse_mercator" variable must be used.
====================================================
;---Get the source lat/lon grid
tas = f->tasmax(0,0,:,:)
lat2d = f->grid_latitude
lon2d = f->grid_longitude
printMinMax(lat2d,0)
printMinMax(lon2d,0)
itm = f->transverse_mercator
print(itm)
print("itm at latitude_of_projection_origin="+itm at latitude_of_projection_origin
)
print("itm at longitude_of_central_meridian="+itm at longitude_of_central_meridian
)
; clarity
lat_shift = itm at latitude_of_projection_origin
lon_shift = itm at longitude_of_central_meridian
; apply 'shift'
lat2d = lat2d + lat_shift
lon2d = lon2d + lon_shift
printMinMax(lat2d,0)
printMinMax(lon2d,0)
tas at lat2d = lat2d ; use 'shifted' coordinates
tas at lon2d = lon2d
================
See attached
On Thu, Feb 25, 2021 at 12:00 PM Dave Allured - NOAA Affiliate via ncl-talk
<ncl-talk at mailman.ucar.edu> 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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