anchor.diff:  { stdenv, fetchurl, fetchpatch, unzip, libjpeg, libtiff, zlib
   , postgresql, mysql, libgeotiff, pythonPackages, proj, geos, openssl
   , libpng, sqlite, libspatialite, poppler, hdf4, qhull, giflib, expat
  -, libiconv
  +, libiconv, libxml2
   , netcdfSupport ? true, netcdf, hdf5, curl
   }:
   
  
positive.code:   };
  
    buildInputs = [ unzip libjpeg libtiff libpng proj openssl sqlite
      libspatialite poppler hdf4 qhull giflib expat ]
    ++ (with pythonPackages; [ python numpy wrapPython ])
    ++ stdenv.lib.optional stdenv.isDarwin libiconv
    ++ stdenv.lib.optionals netcdfSupport [ netcdf hdf5 curl ];
  
negative.code:     "--with-proj=${proj}" # optional
      "--with-geos=${geos}/bin/geos-config"# optional
      "--with-hdf4=${hdf4.dev}" # optional
      "--with-xml2=${libxml2.dev}/bin/xml2-config" # optional
      (if netcdfSupport then "--with-netcdf=${netcdf}" else "")
    ];
  
  