Physical grids

There are several grids that are important in ARTS. This document will list some of them and assumptions that are made about them implicitly throughout the codebase.

There are tests available to check these grids when it matters. Some of these tests are enforced by the type-system itself, others are (sometimes optional) runtime checks. Note that breaking these grid rules will likely lead to silent errors in the calculations.

  • Altitude grid.

    An altitude grid is a vector of altitudes, in meters, that defines the vertical grid. If the grid is used to define atmospheric altitude, it is assumed that the elements will all be in ascending order. If the grid is used to define the subsurface, it is assumed that the elements will be in descending order. The range is regardless of sorting [-inf, inf].

  • Latitude grid.

    The latitude grid is a vector of latitudes, in degrees, that defines a horizontal coordinate upon an ellipsoid. It is always in ascending order, and its range is [-90, 90].

    LatGrid validates the latitude grid when constructed or assigned. Invalid data must be regridded before it can be used.

  • Longitude grid.

    The longitude grid is a vector of longitudes, in degrees, that defines a horizontal coordinate upon an ellipsoid. It is always in ascending order, and its range is [-180, 180).

    LonGrid validates the longitude grid when constructed or assigned. Convert longitude conventions and regrid the data as needed before constructing the grid.

  • Frequency grid.

    The frequency grid is a vector of frequencies, in hertz, that defines the spectral grid. It is always in ascending order, and range is (0, inf).

  • Zenith grid.

    The zenith grid is a vector of zenith angles, in degrees, that defines the vertical direction in the atmosphere. It is always in ascending order, and its range is [0, 180].

  • Azimuth grid.

    The azimuth grid is a vector of azimuth angles, in degrees, that defines the horizontal direction in the atmosphere. It is always in ascending order, and its range is FIXME: What are the range we allow [-180, 180) or [0, 360)?.