# API Reference — Planetary reference frames

class skyfield.planetarylib.PlanetaryConstants

  Planetary constants manager.

  You can use this class to build working models of Solar System bodies by loading text planetary constant files and binary orientation kernels. For a full description of how to use this, see Planetary Reference Frames.

  read_text(file)

    Read frame variables from a KPL/FK file.

    Appropriate files will typically have the extension `.tf` or `.tpc` and will define a series of names and values that will be loaded into this object’s `.variables` dictionary.

        >>> from skyfield.api import load
        >>> pc = PlanetaryConstants()
        >>> pc.read_text(load('moon_080317.tf'))
        >>> pc.variables['FRAME_31006_NAME']
        'MOON_PA_DE421'

  read_binary(file)

    Read binary segments descriptions from a DAF/PCK file.

    Binary segments live in `.bpc` files and predict how a body like a planet or moon will be oriented on a given date.

  build_frame_named(name)

    Given a frame name, return a `Frame` object.

  build_frame(integer, _segment=None)

    Given a frame integer code, return a `Frame` object.

  build_latlon_degrees(frame, latitude_degrees, longitude_degrees, elevation_m=0.0)

    Build an object representing a location on a body’s surface.

class skyfield.planetarylib.Frame(center, segment, matrix)

  Planetary constants frame, for building rotation matrices.

  rotation_at(t)

    Return the rotation matrix for this frame at time `t`.

  rotation_and_rate_at(t)

    Return rotation and rate matrices for this frame at time `t`.

    The rate matrix returned is in units of angular motion per day.