[gdal-dev] NetCDF and EASE-2

[Even Rouault]

Chris,

There are 2 issues with this netCDF file:
- the lon,lat indexing is done in a transposed way w.r.t the netCDF 
conventions. That is in this file the fastest varying dimension is the 
latitude, instead of longitude
- the spacing of the lat variable is not constant

I've a somewhat complicated workflow to propose to create a georeferenced 
GeoTIFF file. It assumes you are running GDAL master 3.1.0dev to be able to 
use the gdalmdimtranslate utility

1) Create a tiled geotiff

gdal_translate NETCDF:"SD_20160901.nc":snd_upd out.tif -co TILED=YES

2) Transpose it, and also mirror the values in the x and y directions. I'm not 
sure why this mirroring is needed at all (at least the one in the horizontal 
direction. The one in the version direction might perhaps be explained by a 
north-up vs south-up convention difference between netCDF and GeoTIFF)

gdalmdimtranslate out.tif out2.tif -co TILED=YES \
    -array band=1,transpose=[1,0],view=[::-1,::-1]

(in theory 1. and 2. could be merged in a single step, but doing the 
transposition on the initial netCDF file will be very inefficient. Doing it on 
a source tiled file is the best)

3) Create a out2.tif.aux.xml file with the following content

<PAMDataset>
  <Metadata domain="GEOLOCATION">
    <MDI key="LINE_OFFSET">0</MDI>
    <MDI key="LINE_STEP">1</MDI>
    <MDI key="PIXEL_OFFSET">0</MDI>
    <MDI key="PIXEL_STEP">1</MDI>
    <MDI key="SRS">EPSG:4326</MDI>
    <MDI key="X_BAND">1</MDI>
    <MDI key="X_DATASET">NETCDF:"SD_20160901.nc":lon</MDI>
    <MDI key="Y_BAND">1</MDI>
    <MDI key="Y_DATASET">NETCDF:"SD_20160901.nc":lat</MDI>
  </Metadata>
</PAMDataset>

4) Warp it:

gdalwarp out2.tif out3.tif -overwrite -co TILED=YES

Even

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