To cite package rtop in publications use:

Skoien, J. O., Bloschl, G., Laaha, G., Pebesma, E., Parajka, J., Viglione, A., 2014. Rtop: An R package for interpolation of data with a variable spatial support, with an example from river networks. Computers & Geosciences, 67.

Corresponding BibTeX entry:

  @Article{,
    title = {Rtop: An R package for interpolation of data with a
      variable spatial support, with an example from river networks},
    author = {J. O. Skoien and G. Bloschl and G. Laaha and E. Pebesma
      and J. Parajka and A. Viglione},
    journal = {Computers & Geosciences},
    year = {2014},
  }