# Coordinate Frame Transforms
The `satkit.frametransform` module provides functions for transforming between various coordinate
frames used in satellite tracking and orbit determination. These include multiple variations of "inertial"
coordinate frames, and multiple versions of "Earth-fixed" coordinate frames.
Some notes:
- Most of the algorithms in this module are from the book "Fundamentals of Astrodynamics and Applications" by David Vallado.
- The frame transforms are defined as arbitrary rotations in a 3-dimensional space. The rotations are a function of time, and are represented as quaternions.
- The rotation from the Geocentric Celestial Reference Frame (GCRF) to the Earth-Centered Inertial (ECI) frame is defined by the International Astronomical Union (IAU), available at <https://www.iers.org/>. See IERS Technical Note 36 for the latest values.
::: satkit.frametransform