[GRASS-user] Cannot read NetCDF with 'semi_major_axis' or 'inverse_flattening'

[Ken Mankoff]

Ok - just to clear this up and shut down this thread. It turns out it is
EPSG:3411 but was reported as 3413. I can import (with -o) into a 3411
location, and then reproject.

Cheers,

  -k.

On Sun, Jul 25, 2021 at 8:45 PM Ken Mankoff <mankoff at gmail.com> wrote:

> Hi Stefan,
>
> Thanks for the hint. I often use '-o'. In this case after discussion with
> the data provider it turns out that it was not EPSG:3413 but instead some
> custom projection, even though part of the NetCDF file reported EPSG:3413
> in the metadata.
>
> Unfortunately r.import does not work. I get the errors below. Given the
> 0..3..6..9... it appears to import something, but no raster exists when the
> command finishes.
>
> r.import input=NetCDF:file.nc:surface output=surface
> WARNING: Datum <unnamed> not recognised by GRASS and no parameters found
> WARNING: Projection of dataset does not appear to match current location.
>
> Location PROJ_INFO is:
> name: WGS 84 / NSIDC Sea Ice Polar Stereographic North
> datum: wgs84
> ellps: wgs84
> proj: stere
> lat_0: 90
> lat_ts: 70
> lon_0: -45
> x_0: 0
> y_0: 0
> no_defs: defined
> init: EPSG:3413
>
> Dataset PROJ_INFO is:
> name: unnamed
> a: 6378273
> es: 0.006693883000000017
> proj: stere
> lat_0: 90
> lat_ts: 70
> lon_0: -45
> x_0: 0
> y_0: 0
> no_defs: defined
>
> ERROR: datum
>
> WARNING: Datum <unnamed> not recognised by GRASS and no parameters found
> WARNING: Datum <unnamed> not recognised by GRASS and no parameters found
> Importing raster map <surface>...
>
> 0..3..6..9..12..15..18..21..24..27..30..33..36..39..42..45..48..51..54..57..60..63..66..69..72..75..78..81..84..87..90..93..96..99..100
> ERROR: Unable to open element file <windows> for
> <tmp.r.import.3257873 at PERMANENT>
> ERROR: Unable to get reprojected map extent
>
>
>   -k.
>
>
>
> On Sat, Jul 24, 2021 at 2:19 PM Stefan Blumentrath <
> Stefan.Blumentrath at nina.no> wrote:
>
>> Hei Ken,
>>
>> Did you try the -o flag ("Override projection check (use current
>> location's projection)
>> Assume that the dataset has same projection as the current location")?
>> https://grass.osgeo.org/grass78/manuals/r.external.html
>> As the error message suggests?
>>
>> If you are sure that projections in fact match, a mismatch in CRS
>> description can be overridden that way, without modifying the input file.
>>
>> Alternatively, you can use r.import to reproject while converting to
>> GRASS format or you create a new location...
>>
>> Cheers
>> Stefan
>>
>>
>> -----Original Message-----
>> From: grass-user <grass-user-bounces at lists.osgeo.org> On Behalf Of Ken
>> Mankoff
>> Sent: fredag 23. juli 2021 19:33
>> To: GRASS user list <grass-user at lists.osgeo.org>
>> Subject: [GRASS-user] Cannot read NetCDF with 'semi_major_axis' or
>> 'inverse_flattening'
>>
>> Hello list,
>>
>> I have been given an updated NetCDF file - everything is the same as the
>> old version except there are two new attributes in the 'mapping' variable:
>>
>>         char mapping ;
>>                 mapping:geoid = "eigen-6c4" ;
>>                 mapping:grid_mapping_name = "polar_stereographic" ;
>>                 mapping:latitude_of_projection_origin = 90. ;
>>                 mapping:standard_parallel = 70. ;
>>                 mapping:straight_vertical_longitude_from_pole = -45. ;
>>                 mapping:semi_major_axis = 6378273. ;
>>                 mapping:inverse_flattening = 298.27940504282 ;
>>                 mapping:false_easting = 0. ;
>>                 mapping:false_northing = 0. ;
>>                 mapping:_Storage = "contiguous" ;
>>
>>
>> Specifically:
>>                 mapping:semi_major_axis = 6378273. ;
>>                 mapping:inverse_flattening = 298.27940504282 ;
>>
>> When I try to load this file with:
>>
>> r.external source=netCDF:file.nc:surface output=surface
>>
>> I get this error:
>>
>> WARNING: Datum <unnamed> not recognised by GRASS and no parameters found
>> ERROR: Projection of dataset does not appear to match current location.
>>
>> Location PROJ_INFO is:
>> name: WGS 84 / NSIDC Sea Ice Polar Stereographic North
>> datum: wgs84
>> ellps: wgs84
>> proj: stere
>> lat_0: 90
>> lat_ts: 70
>> lon_0: -45
>> x_0: 0
>> y_0: 0
>> no_defs: defined
>> init: EPSG:3413
>>
>> Dataset PROJ_INFO is:
>> name: unnamed
>> a: 6378273
>> es: 0.006693883000000017
>> proj: stere
>> lat_0: 90
>> lat_ts: 70
>> lon_0: -45
>> x_0: 0
>> y_0: 0
>> no_defs: defined
>>
>> ERROR: datum
>>
>> In case of no significant differences in the projection definitions, use
>> the -o flag to ignore them and use current location definition.
>> Consider generating a new location from the input dataset using the
>> 'location' parameter.
>>
>>
>> If I remove thos two attributes (semi_major_axis and inverse_flattening)
>> with:
>>
>> ncatted -O -h -a semi_major_axis,mapping,d,l,6378273 -a
>> inverse_flattening,mapping,d,f,298.27940504282 file.nc foo.nc
>>
>> And then try to read in the data, it works.
>>
>> Is there some reason that those two attributes make it difficult to load
>> the data in GRASS? Is there a better work-around than removing them? The
>> documented projection of the data has not changed, only some of the
>> metadata.
>>
>> Versions:
>> gdal 3.0.4
>> grass 7.8.2
>>
>> Thank you,
>>
>>    -k.
>>
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