Voronoi diagram visualizations. There are three types:
        
            1. **vor**: Voronoi diagram of the Solar Horizont.
            2. **freq**: Frequency of Sun positions in t in the Voronoi
                diagram of the Solar Horizont.
            3. **data**: Accumulated time integral of the data projected 
                in the Voronoi diagram of the Solar Horizont.
        
        :param which: Type of visualization.
        :type which: str
        :returns: None

def vor_plot(self, which='vor'):
        """
        Voronoi diagram visualizations. There are three types:
        
            1. **vor**: Voronoi diagram of the Solar Horizont.
            2. **freq**: Frequency of Sun positions in t in the Voronoi
                diagram of the Solar Horizont.
            3. **data**: Accumulated time integral of the data projected 
                in the Voronoi diagram of the Solar Horizont.
        
        :param which: Type of visualization.
        :type which: str
        :returns: None
        """
        import matplotlib.cm as cm
        import matplotlib.pyplot as plt
        sm = self.SM
        if sm.light_vor is None:
            raise ValueError('The computation has not been made yet')

        if which is 'vor':
            title = 'Voronoi diagram of the Solar Horizont'
            ax = sm.vor_surf.plot2d('b', alpha=0.15, ret=True, title=title)
            ax.scatter(sm.azimuth_zenit[:, 0],sm.azimuth_zenit[:, 1], c='k')
            ax.scatter(sm.vor_centers[:, 0], sm.vor_centers[:,1],
                        s = 30, c = 'red')
            ax.set_xlabel('Solar Azimuth')
            ax.set_ylabel('Solar Zenit')
            plt.show()

        elif which is 'freq':
            cmap = cm.Blues
            title = 'Frequency of Sun positions in the Voronoi diagram '+\
                     'of the Solar Horizont'
            ax = sm.vor_surf.plot2d(sm.vor_freq, cmap=cmap, alpha=0.85, 
                                    colorbar=True, title=title, ret=True,
                                    cbar_label='    Freq')
            ax.set_xlabel('Solar Azimuth')
            ax.set_ylabel('Solar Zenit')
            plt.show()
            
        elif which is 'data':
            cmap = cm.YlOrRd
            title = 'Data projected in the Voronoi diagram of the'+\
                    ' Solar Horizont'
            data = sm.proj_vor/sm.vor_freq
            proj_data = data*100/data.max()
            ax = sm.vor_surf.plot2d(proj_data, alpha=0.85, cmap=cmap,
                                    colorbar=True, title=title, ret=True,
                                    cbar_label='%')
            ax.set_xlabel('Solar Azimuth')
            ax.set_ylabel('Solar Zenit')
            plt.title('max = '+str(data.max())+' kilounits*hour')
            plt.show()
            
        else:
            raise ValueError('Invalid plot '+which)