@misc{indiciae06c2aba00050,
  title = {Computer program to predict visibility of global positioning system (GPS) satellites using an IBM-PC or compatible microcomputer},
  author = {J. T. Gann},
  year = {1987},
  doi = {10.3133/ofr87274},
  url = {https://pubs.usgs.gov/publication/ofr87274},
  note = {Source identifier: ofr87274}
}