Problems with plotting data in RADOLAN (polar stereographic projection) #1840

ZofiaBaldysz · 2022-09-28T16:13:08Z

ZofiaBaldysz
Sep 28, 2022

Hi,
I have a NetCDF file with precipitation data saved in RADOLAN Grid (Polar Stereographic Projection) and I have difficulties plotting these data using plot_data_plane tool.
By inspecting a NetCDF CF documentation (https://cfconventions.org/cf-conventions/cf-conventions.html#polar-stereographic) I found that necessary projection elements for Polar Stereographic are either standard_parallel (EPSG 9829) or scale_factor_at_projection_origin (EPSG 9810).
However , when I’m using scale_factor from https://docs.wradlib.org/en/stable/notebooks/radolan/radolan_grid.html , (which according to NetCDF CF documentation should be ok, because it is bigger than 0, scale_factor_at_projection_origin > 0.0) I got information about unexpected value:

NcCfFile::get_grid_mapping_polar_stereographic() -> Unexpected attribute value of 0.9 for the scale_factor_at_projection_origin attribute of the RADOLAN_grid variable.

When I’m creating NetCDF file without scale_factor_at_projection_origin, and instead of this I’m setting standard_paralell, the METPlus gives me error:

ERROR : get_nc_var_att_double() -> Cannot get "scale_factor_at_projection_origin" from RADOLAN_grid variable.

Is there any possibility to add such variables/attributes of polar stereographic projection to the netCDF file, to make it readable by METPlus?

Thanks,
Zofia

ncdump of my file:

dimensions:
        time = 864 ;
        y = 1100 ;
        x = 900 ;
variables:
        int time(time) ;
                time:standard_name = "time" ;
                time:long_name = "time minutes since 2021-07-13T00:00:00.000000000" ;
                time:units = "minutes since 2021-07-13T00:00:00.000000000" ;
        int RADOLAN_grid ;
                RADOLAN_grid:grid_mapping_name = "polar_stereographic" ;
                RADOLAN_grid:projection = "polar_stereographic" ;
                RADOLAN_grid:straight_vertical_longitude_from_pole = 10 ;
                RADOLAN_grid:latitude_of_projection_origin = 90 ;
                RADOLAN_grid:longitude_of_projection_origin = 10 ;
                RADOLAN_grid:horizontal_datum_name = "Radolan_Kugel" ;
                RADOLAN_grid:standard_parallel = 10 ;
                RADOLAN_grid:false_easting = 0 ;
                RADOLAN_grid:false_northing = 0 ;
                RADOLAN_grid:semi_major_axis = 6370040 ;
                RADOLAN_grid:semi_minor_axis = 6370040 ;
                RADOLAN_grid:crs_wkt = "PROJCS[\"Radolan Projection\",\n    GEOGCS[\"Radolan Coordinate System\",\n        DATUM[\"Radolan_Kugel\",\n            SPHEROID[\"Erdkugel\",6370040,0]],\n        PRIMEM[\"Greenwich\",0,\n            AUTHORITY[\"EPSG\",\"8901\"]],\n        UNIT[\"degree\",0.0174532925199433,\n            AUTHORITY[\"EPSG\",\"9122\"]]],\n    PROJECTION[\"Polar_Stereographic\"],\n    PARAMETER[\"latitude_of_origin\",60],\n    PARAMETER[\"central_meridian\",10],\n    PARAMETER[\"false_easting\",0],\n    PARAMETER[\"false_northing\",0],\n    UNIT[\"kilometre\",1000,\n        AUTHORITY[\"EPSG\",\"9036\"]],\n    AXIS[\"Easting\",SOUTH],\n    AXIS[\"Northing\",SOUTH]]" ;
        double lat(y, x) ;
                lat:standard_name = "latitude" ;
                lat:long_name = "latitude" ;
                lat:units = "degrees_north" ;
                lat:coorindates = "lat lon" ;
        double lon(y, x) ;
                lon:standard_name = "longitude" ;
                lon:long_name = "longitude" ;
                lon:units = "degrees_east" ;
                lon:coordinates = "lat lon" ;
        double y(y) ;
                y:standard_name = "projection_y_coordinate" ;
                y:long_name = "RADOLAN Grid y coordinate of projection" ;
                y:units = "km" ;
        double x(x) ;
                x:standard_name = "projection_x_coordinate" ;
                x:long_name = "RADOLAN Grid y coordinate of projection" ;
                x:units = "km" ;
        float PREC(time, y, x) ;
                PREC:_FillValue = NaNf ;
                PREC:standard_name = "rainfall_amount" ;
                PREC:long_name = "rainfall amount" ;
                PREC:description = "accumulated rainfall amount" ;
                PREC:units = "kg m-2" ;
                PREC:grid_mapping = "RADOLAN_grid" ;
                PREC:coordinates = "lat lon" ;

// global attributes:
                :TITLE = "Radar rainfall" ;
                :Conventions = "CF-1.7" ;

Answered by hsoh-u

Nov 29, 2022

This was not included to beta5. It needs more tests because there are two types of polar stereographics (spherical earth and ellipsoidal earth). MET only supports the spherical earth. The data for NSIDC Sea Ice Edge is the ellipsoidal earth

        char crs ;
                crs:grid_mapping_name = "polar_stereographic" ;
                crs:straight_vertical_longitude_from_pole = -45. ;
                crs:false_easting = 0. ;
                crs:false_northing = 0. ;
                crs:latitude_of_projection_origin = 90. ;
                crs:standard_parallel = 70. ;
                crs:long_name = "NSIDC_NH_PolarStereo_25km" ;
                crs:longitude_of_prime_meridian = 0. ;
  …

View full answer

CPKalb · 2022-09-29T21:24:42Z

CPKalb
Sep 29, 2022
Collaborator

Hi Zofia:

We recently discovered a bug in the way MET parses Polar Stereographic grids from CF-compliant NetCDF files. The bug is originally described here. Specifically, there were two issues:

longitude_of_projection_origin is NOT required.
Either scale_factor_at_projection_origin or standard_parallel may be specified, but MET is not parsing/interpreting the latter.

Your second error is due to number 2. It should be reading either scale_factor_at_projection_origin or standard_parallel, but it is not parsing/interpreting the standard_parallel. We have a bugfix issue (dtcenter/MET#2218) in MET to correct this, but it has not been merged into MET yet. Please feel free to comment directly on the issue to let us know if/when it's needed.

I'm not familiar with how MET uses the scale_factor_at_projection_origin, so would need to check with others here, if that is needed as well.

Christina

4 replies

ZofiaBaldysz Sep 30, 2022
Author

Hi Christina,
thank you very much for quick response. I think the problem is not exactly the same. If I provide only standard_parallel the MET requires also scale_factor_at_projection_origin. But, if provide only scale_factor_at_projection_origin I get the error message about wrong value. I found that if I provide value 1, it works, but then it is different projection. According to the projection details, the scale factor should be 0.93301270189 but there is no way how to put it into MET. It seems, that MET doesn't allow to provide the value below 1 (just my insights), while NETCDF CF standard allows these values to be above 0.

Zofia

CPKalb Oct 3, 2022
Collaborator

Hi Zofia:

Thanks for clarifying. MET should not require both the standard_parallel and scale_factor_at_projection_origin. It should only require one or the other.

Do you have a sample data file that could be uploaded to our ftp. It would be helpful for us to have a sample file that we could use to test the changes/enhancements that we are making to MET for polar stereographic data.

Christina

JohnHalleyGotway Oct 10, 2022
Maintainer

@ZofiaBaldysz and @CPKalb, @hsoh-u is working on the a bugfix including the handling of this scale factor of 0.9.

I went hunting for a sample data file on our ftp site, but couldn't find one.

@ZofiaBaldysz can you please send us a sample data file we can use for testing? It can be uploaded here. And then respond here so we know to go look for it.

Thanks.

ZofiaBaldysz Oct 10, 2022
Author

@CPKalb and @JohnHalleyGotway I apologize for the delayed answer.
I've prepared some sample files but I will describe the problem again to understand my issue better.
In NETCDF CF documentation (https://cfconventions.org/cf-conventions/cf-conventions.html#polar-stereographic), there is information that polar stereographic projection requires the following attributes:

straight_vertical_longitude_from_pole
latitude_of_projection_origin - Either +90. or -90.
Either standard_parallel (EPSG 9829) or scale_factor_at_projection_origin (EPSG 9810)
false_easting - This parameter is optional (default is 0)
false_northing - This parameter is optional (default is 0)

First issue:
When I provided straight_vertical_longitude_from_pole, latitude_of_projection_origin and standard_parallel and ran:
plot_data_plane radolan.nc radolan.ps 'name="PREC"; level="(0,*,*)";'
I obtained the error:
get_nc_var_att_double() -> Cannot get "longitude_of_projection_origin" from RADOLAN_grid variable.

Second issue:
To my previous case I added longitude_of_projection_origin and I got error:
get_nc_var_att_double() -> Cannot get "scale_factor_at_projection_origin" from RADOLAN_grid variable.

Third issue:
To my second issue I added scale_factor_at_projection_origin equal 0.93301270189 and I got:
NcCfFile::get_grid_mapping_polar_stereographic() -> Unexpected attribute value of 0.933013 for the scale_factor_at_projection_origin attribute of the RADOLAN_grid variable.
but in NETCDF CF documentation, we can find that the scale factor can be > 0.0

Fourth issue:
I removed standard_parallel and left only scale_factor_at_projection_origin and I obtained the same error:
NcCfFile::get_grid_mapping_polar_stereographic() -> Unexpected attribute value of 0.933013 for the scale_factor_at_projection_origin attribute of the RADOLAN_grid variable.

I've prepared two example files:
radolan_sp.nc - issue two (only standard_parallel)
radolan_sp_sf.nc - issue three (standard_parallel and scale_factor_at_projection_origin)
I will try to upload them to your ftp server.

Thanks,
Zofia

hsoh-u · 2022-10-13T14:58:51Z

hsoh-u
Oct 13, 2022
Collaborator

The uploaded files are not recognized by MET and ncdump. Would you convert it to HDF5 or NetCDF files?

1 reply

ZofiaBaldysz Oct 13, 2022
Author

The files are already in NetCDF. Maybe something went wrong with data upload. I've uploaded them once again.

netcdf radolan_sf {
dimensions:
        time = 1 ;
        y = 1100 ;
        x = 900 ;
variables:
        int time(time) ;
                time:standard_name = "time" ;
                time:long_name = "time minutes since 2020-01-01T00:00:00.000000000" ;
                time:units = "minutes since 2020-01-01T00:00:00.000000000" ;
        int RADOLAN_grid ;
                RADOLAN_grid:grid_mapping_name = "polar_stereographic" ;
                RADOLAN_grid:projection = "polar_stereographic" ;
                RADOLAN_grid:straight_vertical_longitude_from_pole = 10 ;
                RADOLAN_grid:latitude_of_projection_origin = 90 ;
                RADOLAN_grid:longitude_of_projection_origin = 10 ;
                RADOLAN_grid:scale_factor_at_projection_origin = 0.93301270189 ;
                RADOLAN_grid:false_easting = 0 ;
                RADOLAN_grid:false_northing = 0 ;
                RADOLAN_grid:semi_major_axis = 6370040 ;
                RADOLAN_grid:semi_minor_axis = 6370040 ;
        double lat(y, x) ;
                lat:standard_name = "latitude" ;
                lat:long_name = "latitude" ;
                lat:units = "degrees_north" ;
                lat:coorindates = "lat lon" ;
        double lon(y, x) ;
                lon:standard_name = "longitude" ;
                lon:long_name = "longitude" ;
                lon:units = "degrees_east" ;
                lon:coordinates = "lat lon" ;
        double y(y) ;
                y:standard_name = "projection_y_coordinate" ;
                y:long_name = "RADOLAN Grid y coordinate of projection" ;
                y:units = "km" ;
        double x(x) ;
                x:standard_name = "projection_x_coordinate" ;
                x:long_name = "RADOLAN Grid y coordinate of projection" ;
                x:units = "km" ;
        float PREC(time, y, x) ;
                PREC:_FillValue = NaNf ;
                PREC:standard_name = "rainfall_amount" ;
                PREC:long_name = "rainfall amount" ;
                PREC:description = "accumulated rainfall amount" ;
                PREC:units = "kg m-2" ;
                PREC:grid_mapping = "RADOLAN_grid" ;
                PREC:coordinates = "lat lon" ;

// global attributes:
                :TITLE = "Radar rainfall" ;
                :Conventions = "CF-1.7" ;
}

hsoh-u · 2022-10-13T17:53:16Z

hsoh-u
Oct 13, 2022
Collaborator

Thank you, new files are good

0 replies

ZofiaBaldysz · 2022-11-06T14:26:23Z

ZofiaBaldysz
Nov 6, 2022
Author

Hi!
Just wanted to check if there is any news regarding to our polar stereographic issue?
Thanks,
Zofia

0 replies

hsoh-u · 2022-11-07T00:49:20Z

hsoh-u
Nov 7, 2022
Collaborator

We made some progress and we aim to release at the next beta.

0 replies

hsoh-u · 2022-11-17T20:34:43Z

hsoh-u
Nov 17, 2022
Collaborator

The scale_factor is computed from the standard_parallel. Plot By MET (will be available with beta 5):

Plot By other tool:

0 replies

hsoh-u · 2022-11-29T16:56:55Z

hsoh-u
Nov 29, 2022
Collaborator

This was not included to beta5. It needs more tests because there are two types of polar stereographics (spherical earth and ellipsoidal earth). MET only supports the spherical earth. The data for NSIDC Sea Ice Edge is the ellipsoidal earth

        char crs ;
                crs:grid_mapping_name = "polar_stereographic" ;
                crs:straight_vertical_longitude_from_pole = -45. ;
                crs:false_easting = 0. ;
                crs:false_northing = 0. ;
                crs:latitude_of_projection_origin = 90. ;
                crs:standard_parallel = 70. ;
                crs:long_name = "NSIDC_NH_PolarStereo_25km" ;
                crs:longitude_of_prime_meridian = 0. ;
                crs:semi_major_axis = 6378273. ;
                crs:inverse_flattening = 298.279411123064 ;

2 replies

hsoh-u Jan 31, 2023
Collaborator

We aim for the MET v11.0.1 bugfix release.
Regridding a spherical earth with the parallel standard instead of scale factor (input: radolan_sp.nc):

Regridding an ellipsoidal earth with the parallel standard instead of scale factor and additional attributes (input: NSIDC0081_SEAICE_PS_N25km_20220723_v2.0.nc):

                crs:standard_parallel = 70. ;
                crs:false_easting = 0. ;
                crs:false_northing = 0. ;
                ...
                crs:semi_major_axis = 6378273. ;
                crs:inverse_flattening = 298.279411123064 ;

JohnHalleyGotway Mar 31, 2023
Maintainer

Marking as answered since the fix was provided in the 11.0.1 bugfix release.

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Problems with plotting data in RADOLAN (polar stereographic projection) #1840

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Problems with plotting data in RADOLAN (polar stereographic projection) #1840

ZofiaBaldysz Sep 28, 2022

Replies: 7 comments · 7 replies

CPKalb Sep 29, 2022 Collaborator

ZofiaBaldysz Sep 30, 2022 Author

CPKalb Oct 3, 2022 Collaborator

JohnHalleyGotway Oct 10, 2022 Maintainer

ZofiaBaldysz Oct 10, 2022 Author

hsoh-u Oct 13, 2022 Collaborator

ZofiaBaldysz Oct 13, 2022 Author

hsoh-u Oct 13, 2022 Collaborator

ZofiaBaldysz Nov 6, 2022 Author

hsoh-u Nov 7, 2022 Collaborator

hsoh-u Nov 17, 2022 Collaborator

hsoh-u Nov 29, 2022 Collaborator

hsoh-u Jan 31, 2023 Collaborator

JohnHalleyGotway Mar 31, 2023 Maintainer

ZofiaBaldysz
Sep 28, 2022

Replies: 7 comments 7 replies

CPKalb
Sep 29, 2022
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ZofiaBaldysz Sep 30, 2022
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CPKalb Oct 3, 2022
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JohnHalleyGotway Oct 10, 2022
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ZofiaBaldysz Oct 10, 2022
Author

hsoh-u
Oct 13, 2022
Collaborator

ZofiaBaldysz Oct 13, 2022
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hsoh-u
Oct 13, 2022
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ZofiaBaldysz
Nov 6, 2022
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hsoh-u
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hsoh-u
Nov 17, 2022
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hsoh-u
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hsoh-u Jan 31, 2023
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