# ARTS built-in documentation server

## Workspace Method ppathFromRtePos2

### Description

Determines the propagation path from rte_pos2 to rte_pos.
The propagation path linking rte_pos and rte_pos2 is calculated
and returned. The method determines the path in a pure numerical
manner, where a simple algorithm is applied. The task is to find
the value of rte_los (at rte_pos) linking the two positions.
See the user guide for a description of the search algorithm,
including a more detailed definition of *za_accuracy*,
*pplrt_factor* and *pplrt_lowest*.
The standard application of this method should be to radio link
calculations, where rte_pos2 corresponds to a transmitter, and
rte_pos to the receiver/sensor.
The details of the ray tracing is controlled by ppath_step_agenda
as usual.

**Authors: **Patrick Eriksson

### Synopsis

ppathFromRtePos2( | ppath, rte_los, ppath_lraytrace, ppath_step_agenda, atmosphere_dim, p_grid, lat_grid, lon_grid, z_field, f_grid, refellipsoid, z_surface, rte_pos, rte_pos2, ppath_lmax, za_accuracy, pplrt_factor, pplrt_lowest ) |

### Variables

OUT | ppath | (Ppath) | The propagation path for one line-of-sight. |

OUT+IN | rte_los | (Vector) | A line-of-sight for (complete) radiative transfer calculations. |

OUT+IN | ppath_lraytrace | (Numeric) | Maximum length of ray tracing steps when determining propagation paths. |

IN | ppath_step_agenda | (Agenda) | Agenda calculating a propagation path step. |

IN | atmosphere_dim | (Index) | The atmospheric dimensionality (1-3). |

IN | p_grid | (Vector) | The pressure grid. |

IN | lat_grid | (Vector) | The latitude grid. |

IN | lon_grid | (Vector) | The longitude grid. |

IN | z_field | (Tensor3) | The field of geometrical altitudes. |

IN | f_grid | (Vector) | The frequency grid for monochromatic pencil beam calculations. |

IN | refellipsoid | (Vector) | Reference ellipsoid. |

IN | z_surface | (Matrix) | The surface altitude. |

IN | rte_pos | (Vector) | A geographical position for starting radiative transfer calculations. |

IN | rte_pos2 | (Vector) | A second geographical position to define the geometry for radiative transfer calculations. |

IN | ppath_lmax | (Numeric) | Maximum length between points describing propagation paths. |

GIN | za_accuracy | (Numeric, Default: 2e-5) | Required accuracy, in form of the maximum allowed angular off-set [deg]. |

GIN | pplrt_factor | (Numeric, Default: 5) | The factor with which ppath_lraytrace is decreased if no solution is found. |

GIN | pplrt_lowest | (Numeric, Default: 0.5) | Lowest value ppath_lraytrace to consider. The calculations are halted if this length is passed. |