Calibration Tutorial for ORB-SLAM3 v1.0
Juan J. Gómez Rodríguez, Carlos Campos, Juan D. Tardós
December 22, 2021
1 Introduction
This document contains a brief explanation of visual and visual-inertial calibration for
ORB-SLAM3 v1.0. In this version we introduce a new calibration file format whose main
novelties are:
• Improved readability with consistent naming.
• Option for internal rectification of stereo images.
• Option for internal resizing of the input images.
Some examples of use of the new calibration fromat can be found at directory Examples.
Although we recommend using the new file format, for the user convenience, we main-
tain compatibility with the file format used in previous versions, whose examples are in
directory Examples_old.
2 Reference systems and extrinsic parameters
Extrinsic calibration consists of the set of parameters which define how different sensors
are geometrically related. The most complex case is the stereo-inertial configuration,
shown in figure 1, where we define the following reference frames:
• World (W): Defines a fixed reference system, whose z
W
axis points in opposite
direction of the gravity vector g. Translation and yaw are freely set by the SLAM
system and remain fixed once initialized. In the pure visual case, the world reference
is set to the first camera pose.
• Body (B): This is the optimizable reference and is attached to the IMU. We assume
the gyroscope and the accelerometer share the same reference system. Body pose
T
WB
and velocity v
B
expressed in W are the optimizable variables.
• Cameras (C
1
and C
2
): These are coincident with the optical center of the cameras,
with z
C
pointing forward along the optical axis, y
C
pointing down and x
C
pointing
to the right, both aligned with image directions u and v.
1
