code: function(dvi, di) {
      var dim = msg.structure.dimensions.observation[di];
      // Calculate the key position for the dimension index
      var pos = dimPosition(dim);
      // Update the obskey with the dimension value
      obsKey[pos] = dim.values[dvi].id;
    }
docs: Updates the obsKey array of dimension ids e.g. [ 'M', 'FI', 'P' ] with observation level dimension values. Gets the dimension value index and dimension index as arguments