# ARTS built-in documentation server

## Workspace Method ppath_fieldFromDownUpLimbGeoms

### Description

Computes ppath_field from "standalone" sensors looking upwards from 0 m altitude with zenith angles range [0, 90], downwards from the top of the atmosphere covering the zenith angle range from 180 degrees to the surface tangent minus 1e-4 degrees, and through the limb covering at the same position as the downwards looking sensor covering the zenith angle range from the surface tangent plus 1e-4 degrees to 90 degrees minus 1e-4 degrees. The top of the atmosphere is from z_field (-1, 0, 0) [python range notation]. The field will consist of 3 * nz arrays structured as [up, limb, down] The intent of this function is to generate a field so that calculations of ppvar_iy of all the fields will cover the zenith angle space of all positions in z_field. Only works for atmosphere_dim 1, spherical planets, and ppath_lmax < 0

**Authors: **Richard Larsson

### Synopsis

ppath_fieldFromDownUpLimbGeoms( | ppath_field, ppath_agenda, ppath_lmax, ppath_lraytrace, atmgeom_checked, z_field, f_grid, cloudbox_on, cloudbox_checked, ppath_inside_cloudbox_do, rte_pos, rte_los, rte_pos2, refellipsoid, atmosphere_dim, nz ) |

### Variables

OUT | ppath_field | (ArrayOfPpath) | An array meant to build up the necessary geometries for radiative field calculations. |

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

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. |

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

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

GIN | nz | (Index, Default: 3) | Number of zenith angles per position |