docs: def get_indices(self, k):
          """ Get indices of theta vector that have k as first corner.
          
          :param k: Index of corner.
  
          :return indices_rays: Indices of ray angles in theta vector.
          :return indices_triangles: Indices of triangle angles in theta vector.
          :return corners_rays: List of corners of ray angles.
          :return angles_rays: List of corners of triangles angles.
          """
          indices_rays = []
          indices_triangles = []
          corners_rays = []
          angles_rays = []
          for t, triangle in enumerate(self.corners):
              if triangle[0] == k:
                  indices_rays.append(t)
                  corners_rays.append(triangle)
                  angles_rays.append(self.theta[t])
              else:
                  indices_triangles.append(t)
          np_corners_rays = np.vstack(corners_rays)
          np_angles_rays = np.vstack(angles_rays).reshape((-1, ))
          return indices_rays, indices_triangles, np_corners_rays, np_angles_rays