docs: def plot2d(self, c_poly='default', alpha=1, cmap='default', ret=False, 
                 title=' ', colorbar=False, cbar_label=''):
          """
          Generates a 2D plot for the z=0 Surface projection.
          
          :param c_poly: Polygons color.
          :type c_poly: matplotlib color
          :param alpha: Opacity.
          :type alpha: float
          :param cmap: colormap
          :type cmap: matplotlib.cm
          :param ret: If True, returns the figure. It can be used to add 
              more elements to the plot or to modify it.
          :type ret: bool
          :param title: Figure title.
          :type title: str
          :param colorbar: If True, inserts a colorbar in the figure.
          :type colorbar: bool
          :param cbar_label: Colorbar right label.
          :type cbar_label: str
          :returns: None, axes
          :rtype: None, matplotlib axes
          """
          import matplotlib.pyplot as plt
          import matplotlib.patches as patches
          import matplotlib.cm as cm
          
          paths = [polygon.get_path() for polygon in self]
          domain = self.get_domain()[:, :2]
  
          # Color
          if type(c_poly) == str: # Unicolor
              if c_poly is 'default': c_poly = 'b'
              color_vector = c_poly*len(paths)
              colorbar = False
          else:                  # Colormap
              if cmap is 'default':
                  cmap = cm.YlOrRd
              import matplotlib.colors as mcolors
              normalize = mcolors.Normalize(vmin=c_poly.min(), vmax=c_poly.max())
              color_vector = cmap(normalize(c_poly))
  
          # Plot
          fig = plt.figure(title)
          ax = fig.add_subplot(111)
          for p, c in zip(paths, color_vector):
              ax.add_patch(patches.PathPatch(p, facecolor=c, lw=1, 
                                             edgecolor='k', alpha=alpha))
          ax.set_xlim(domain[0,0],domain[1,0])
          ax.set_ylim(domain[0,1], domain[1,1])
          
          # Colorbar
          if colorbar:
              scalarmappaple = cm.ScalarMappable(norm=normalize, cmap=cmap)
              scalarmappaple.set_array(c_poly)
              cbar = plt.colorbar(scalarmappaple, shrink=0.8, aspect=10)
              cbar.ax.set_ylabel(cbar_label, rotation=0)
  
          if ret: return ax