Opened 7 years ago

Closed 6 years ago

#4514 closed defect (fixed)

netcdf driver does not keep original latitude values for Gaussian grids

Reported by: etourigny Owned by: etourigny
Priority: normal Milestone:
Component: default Version: svn-trunk
Severity: normal Keywords: netcdf, geolocation
Cc: bronaugh

Description

Gaussian grids have non-regular latitude values, but when the difference between pixel spacing is less than 0.1 degree, the geotransform is approximated using the spacing between the first and second pixel.

This may induce small errors in geotransform, and also causes loss of the original values on export.

The ideal fix would be to support 1D GEOLOCATION arrays, but as the netcdf driver does not support 1D rasters, an easier fix is to save the original latitude values for export, and continue with the current approximation to the geotransform.

Attachments (1)

reduce-cgcms.nc (24.3 KB) - added by etourigny 7 years ago.
Gaussian grid with timesteps removed (provided by David Bronaugh)

Download all attachments as: .zip

Change History (3)

Changed 7 years ago by etourigny

Attachment: reduce-cgcms.nc added

Gaussian grid with timesteps removed (provided by David Bronaugh)

comment:1 Changed 7 years ago by etourigny

Cc: bronaugh added

Fixed in trunk (r23982) : netcdf: better support for Gaussian grids - store original latitude values in special Y_VALUES geolocation metadata item and use it for netcdf export

Existing GEOLOCATION arrays mechanism is not used, because the netcdf driver does not support 1D rasters. Instead, a custom Y_VALUES metadata item is used.

Geotransform handling has not changed, but upon export latitude values are copied from Y_VALUES instead of geotransform.

Perhaps there should there be more error checking when exporting, because the geotransform might have changed, and the Y_VALUES metadata might be copied over.

Bounds variables are not addressed, perhaps similar metadata items should be used, or GEOLOCATION bands (would not make sense for time bounds though).

comment:2 Changed 6 years ago by etourigny

Resolution: fixed
Status: newclosed

I am going to close this ticket, as I have applied a workaround some time ago and there has been no activity

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