# ARTS built-in documentation server

## Workspace Method ppathCalcFromAltitude

### Description

Moves rte_pos forwards to near altitude before calling ppathCalc to compute a different ppath. The accuracy-variable gives minimum distance before the input altitude. The forward-moving algorithm calls ppathCalc several times at reduced maximum distances. The intention is to maintain the correct rte_los for a given rte_pos at all altitudes. The method is thus relatively slow, and VERY memory intense at low accuracy. Intended to be used with "tropospheric corrections" from ground geometry. Not well-tested Throws error if no altitude is in line of sight.

**Authors: **Richard Larsson

### Synopsis

ppathCalcFromAltitude( | ppath, ppath_agenda, ppath_lmax, ppath_lraytrace, atmgeom_checked, f_grid, cloudbox_on, cloudbox_checked, ppath_inside_cloudbox_do, rte_pos, rte_los, rte_pos2, altitude, accuracy ) |

### Variables

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

IN | ppath_agenda | (Agenda) | Agenda calculating complete propagation paths. |

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

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

IN | atmgeom_checked | (Index) | OK-flag for the geometry of the model atmosphere. |

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

IN | cloudbox_on | (Index) | Flag to activate the cloud box. |

IN | cloudbox_checked | (Index) | OK-flag for variables associated with the cloudbox. |

IN | ppath_inside_cloudbox_do | (Index) | Flag to perform ray tracing inside the cloudbox. |

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

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

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

GIN | altitude | (Numeric) | Altitude to move forward towards |

GIN | accuracy | (Numeric, Default: 0.5) | Accuracy of altitude |