[gdal-dev] regular grid longlat netcdf without crs meta

[Even Rouault]

Michael,

Le 15/03/2022 à 06:06, Michael Sumner a écrit :
> Hi,
>
> these files don't present to GDAL with a CRS, but it seems not out of 
> place to assume that they can use 'oSRS.SetWellKnownGeogCS("WGS84")', 
> when no other indication is found and there are dimensions 'lon,lat' 
> or 'longitude,latitude'
>
> https://www.ncei.noaa.gov/data/sea-surface-temperature-optimum-interpolation/v2.1/access/avhrr/
>
> An example sds specifically:
>
> /vsicurl/NETCDF:"/vsicurl/https://www.ncei.noaa.gov/data/sea-surface-temperature-optimum-interpolation/v2.1/access/avhrr/202202/oisst-avhrr-v02r01.20220201.nc":sst
>
> Would that be reasonable? Perhaps controlled by an env var? Is there 
> an established control for this I'm missing? (I'm not looking for 
> '-a_srs' or VRT, I want the auto-detection to work for these and many 
> other similar file sources without augmentation).

I wouldn't expose WGS84 by default, because it might be another Earth 
geographic CRS, or even a non-Earth geographic CRS.

Potential solution:

- add a GDAL_NETCDF_DEFAULT_GEOGRAPHIC_CRS configuration option (that 
could be set to EPSG:4326 e.g) that would be used in the situation where 
the netCDF CF attributes to define a geographic CRS, but without the 
actual CRS definition, are not set.

- or, more involved but more powerful, add a configuration file in data/ 
, let's say a netcdf_product_conf.json or whatever, where you would 
define a set of product types, with matching global attributes and their 
values and the corresponding CRS.

e.g (not sure my set of "matching_attributes" is appropriate for your 
use case)

{
     "product_type": {
         "noaa_ncei_oisst": {  // the id of the product here is 
completely arbitrary
             "defining_global_attributes": {
                 "title": "NOAA/NCEI 1/4 Degree Daily Optimum 
Interpolation Sea Surface Temperature (OISST) Analysis, Version 2.1 - 
Final",
                 "geospatial_lat_units": "degrees_north",
                 "geospatial_lon_units": "degrees_east"
             },
             "default_values": {
                 "crs": "EPSG:4326"
             }
         }
     }

}

- or, both the easiest and hardest one, convince the data producer to 
just use the netCDF CF conventions to their full capabilities.

Even

>
> (It's not out of the question that I could submit a PR for this, just 
> flagging discussion in case I'm missing something.)
>
> Thanks.
>
> Best, Mike
>
>
> -- 
> Michael Sumner
> Software and Database Engineer
> Australian Antarctic Division
> Hobart, Australia
> e-mail: mdsumner at gmail.com
>
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-- 
http://www.spatialys.com
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