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I have been working with the following GRIB2 files at https://mrms.ncep.noaa.gov/data/3DZdr/MergedZdr_02.00/. I need to setup a process to convert these to geoJSON polygons. I have tried official tools, GDAL, and broken old repos on GitHub that bring me nowhere.

My goal is to get a command working that inputs a GRIB2 and outputs a geoJSON, in a format close to (or reasonably close, plain-text, anything) to this format :

  {
    "type": "Feature",
    "geometry": {      "type": "Polygon",
      "coordinates": [
        [
          [-75.9404018832492, 42.214059843606286],
          [-75.9376138443044, 42.2149380047364],
          [-75.93727048421295, 42.21432100565146],
          [-75.94007869956438, 42.21347914637607],
          [-75.9404018832492, 42.214059843606286]
        ]
      ]
     },
     "properties": {
        "value": -3.88768
     }
   }

This is all I need. I have tried gdal_translate, ogr2ogr and numerous tools (netCDF tools, python utilities) and I have come to the conclusion that this is not possible or I do not know what I am doing. If the latter is true, I would appreciate someone enlightening me. I was not expecting this to be so difficult. I would post code I have tried, but none of it is likely to make much sense in the context of my question since I have no actual working script at all yet.

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1 Answer 1

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As it turns out, I had used gdal_polygonize but it was giving whole numbers as output, and it appeared that it "wasn't working". In fact, there is a version of gdal_polygonize that will output floating point (https://trac.osgeo.org/gdal/attachment/ticket/4516/gdal_polygonize.py).

Also, on Windows - not using "-q" gives a traceback error which caused even more confusion. With both of these issues resolved, it now works.

The command used was :

gdal_polygonize.py filename.grib2 --float -q -f "geoJSON" out.json layer fieldname

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