[gdal-dev] near identical files being treated differently

[Even Rouault]

Ken,

if you do "gdalinfo --debug on GLMELT_4X5.OCN.nc", you'll see

GDAL_netCDF: Latitude/Y is not equally spaced (with a 0.05% tolerance). 
You may set the GDAL_NETCDF_IGNORE_EQUALLY_SPACED_XY_CHECK configuration 
option to YES to ignore this check

and indeed

$ ncdump -v lat GLMELT_4X5.OCN.nc
[...]
  lat = -89, -86, -82, -78, -74, -70, -66, -62, -58, -54, -50, -46, -42, 
-38,
     -34, -30, -26, -22, -18, -14, -10, -6, -2, 2, 6, 10, 14, 18, 22, 
26, 30,
     34, 38, 42, 46, 50, 54, 58, 62, 66, 70, 74, 78, 82, 86, 89 ;


So you can see the spacing is 4 degree, except for the first and lat 
samples where it is 3. So GDAL cannot report a geotransform matrix for 
such file.

I've just submitted https://github.com/OSGeo/gdal/pull/7113 where GDAL 
will report a GEOLOCATION metadata domain, that can be used by gdalwarp 
to rectify such file

$ gdalinfo autotest/gdrivers/data/netcdf/GLMELT_4X5.OCN.nc

[...]

Geolocation:
   GEOREFERENCING_CONVENTION=PIXEL_CENTER
   LINE_OFFSET=0
   LINE_STEP=1
   PIXEL_OFFSET=0
   PIXEL_STEP=1
   SRS=GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS 
84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AXIS["Latitude",NORTH],AXIS["Longitude",EAST],AUTHORITY["EPSG","4326"]]
   X_BAND=1
X_DATASET=NETCDF:"autotest/gdrivers/data/netcdf/GLMELT_4X5.OCN.nc":lon
   Y_BAND=1
Y_DATASET=NETCDF:"autotest/gdrivers/data/netcdf/GLMELT_4X5.OCN.nc":lat

Even

Le 23/01/2023 à 13:46, Ken Mankoff a écrit :
> wgethttps://portal.nccs.nasa.gov/GISS_modelE/modelE_input_data/GLMELT_4X5.OCN.nc
>
> wgethttps://portal.nccs.nasa.gov/GISS_modelE/modelE_input_data/GLMELT_144X90_gas.OCN.nc

-- 
http://www.spatialys.com
My software is free, but my time generally not.