Extrinsics Configuration File

Download Sample extrinsics.ini Verify Extrinsics

The extrinsics define the three-dimensional relationship (translation and rotation) between the left and right cameras in a stereo camera setup. We parameterize this relationship using Euler angles \(\left( \phi, \theta, \psi \right)\) and a translation vector \(\left( T_1, T_2, T_3 \right)\). Specifically, we assume that the representation of a point \(p\) in the left camera frame \(p_l\) is related to its representation in the right camera frame \(p_r\) by:

\[ \begin{align} p_r &= R \cdot p_l - T \\ &= R_z(\psi) R_y(\theta) R_x(\phi) \cdot p_l - \left[ \begin{array}{c} T_1 \\ T_2 \\ T_3 \end{array} \right] \end{align} \]

that is, \(R\) denotes the 3×3 rotation matrix from the left to the right camera frame, and \(T\) denotes the position of the right camera relative to the left camera, expressed in the right camera frame.

Note that in both the left and right camera frames: - the \(z\)-axis points forward - the \(x\)-axis points to the right - the \(y\)-axis points down

The extrinsics configuration file (extrinsics.ini) is a simple text file containing these values:

phi = 0
theta = 0
psi = 0
T1 = 1
T2 = 0
T3 = 0

!!! We expect angles \(\phi,\theta,\psi\) in degrees, and translations \(T_1,T_2,T_3\) in meters!!!

As a reminder... phi = \(\phi\), theta = \(\theta\), psi = \(\psi\)

Put in words...

  • \(\phi\) denotes the pitch or Euler angle of the left camera in degrees around the x-axis relative to the right camera
  • \(\theta\) denotes the yaw or Euler angle of the left camera in degrees around the y-axis relative to the right camera
  • \(\psi\) denotes the roll or Euler angle of the left camera in degrees around the z-axis relative to the right camera

We strongly recommend that you refer to the Nodar Extrinsics Checker to see a 3D rendering of how we are interpreting your extrinsics:

Verify Extrinsics

Specifically, you should double-check that the rendering matches your actual camera configuration.

You can perform the Initial Calibration routine to get the initial extrinsic parameters between the cameras.