title: plot spatial data from irregular grid
body: <p>I would like to use the <code>rasterVis</code> package to plot contours of spatial data (e.g. using levelplot as in this <a href="https://oscarperpinan.github.io/rastervis/" rel="nofollow noreferrer">example</a>). However, the dataset comes from a <code>NetCDF</code> file with an irregular grid, as below:</p>
  
  <blockquote>
    <p>lon(y,x) lat(y,x) var(y,x)</p>
  </blockquote>
  
  <p>and there is no implication to the projection implied by lon/lat.</p>
  
  <p>Is there a method to plot directly the dataset as raster data
  as in <a href="https://oscarperpinan.github.io/rastervis/" rel="nofollow noreferrer">these</a> figures without interpolation?</p>
  
  <p>The headers of raster data include an extension of the grid and projection specification, which does not fit with my problem. Two-dimensional lon/lat arrays are not recognized by raster as coordinate systems.</p>
  
  <p>Code and plots as in this <a href="https://oscarperpinan.github.io/rastervis/" rel="nofollow noreferrer">example</a> but with <code>netcdf</code> file as:</p>
  
  <pre><code>float lat(y, x) ;
      lat:standard_name = "latitude" ;
      lat:long_name = "Latitude" ;
      lat:units = "degrees_north" ;
      lat:nav_model = "grid_T" ;
  float lon(y, x) ;
      lon:standard_name = "longitude" ;
      lon:long_name = "Longitude" ;
      lon:units = "degrees_east" ;
      lon:nav_model = "grid_T" ;
  float icethic(time_centered, y, x) ;
      icethic:standard_name = "sea_ice_thickness" ;
      icethic:long_name = "Ice thickness (cell average)" ;
      icethic:units = "m" ;
      icethic:online_operation = "average" ;
      icethic:_FillValue = 1.e+20f ;
      icethic:missing_value = 1.e+20f ;
      icethic:coordinates = "time_centered nav_lon nav_lat" ;
  </code></pre>