Isaac Sim Conventions

This section provides a reference for the units, representations, and coordinate conventions used within Omniverse Isaac Sim.

Default Units

Measurement

Units

Notes

Length

Meter

Mass

Kilogram

Time

Seconds

Physics Time-Step

Seconds

Configurable by User. Default is 1/60.

Force

Newton

Frequency

Hertz

Linear Drive Stiffness

\(kg/s^2\)

Angular Drive Stiffness

\((kg*m^2)/(s^2*angle)\)

Linear Drive Damping

\(kg/s\)

Angular Drive Damping

\((kg*m^2)/(s*angle)\)

Diagonal of Inetria

\((kg*m^2)\)

Default Rotation Representations

Quaternions

API

Representation

Isaac Sim Core

(QW, QX, QY, QZ)

USD

(QW, QX, QY, QZ)

PhysX

(QX, QY, QZ, QW)

Dynamic Control

(QX, QY, QZ, QW)

Angles

API

Representation

Isaac Sim Core

Radians

USD

Degrees

PhysX

Radians

Dynamic Control

Radians

..note :: UI elements that show attributes from USD should always display angles in Degrees, even if the value comes from Physics.

Matrix Order

API

Representation

Isaac Sim Core

Row Major

USD

Row Major

World Axes

Omniverse Isaac Sim follows the right-handed coordinate conventions.

_images/isaac_conventions_world_frame.png

Direction

Axis

Notes

Up

+Z

Forward

+X

Default Camera Axes

_images/isaac_conventions_camera_frame.png

Direction

Axis

Notes

Up

+Y

Forward

-Z

Note

Isaac Sim to ROS Conversion: To convert from Isaac Sim Camera Coordinates to ROS Camera Coordinates, rotate 180 degrees about the X-Axis.

Image Frames (Synthetic Data)

Coordinate

Corner

(0,0)

Top Left

Sensor Axes Representation (LiDAR, Cameras)

Cameras in Isaac Sim are subject to three different types of axes definition, depending on the context of use. Here, we introduce the three conventions and how it’s used in different contexts.

World Axes

The world axes uses the +X forward, +Z up convention. The origin of the world prim is always represented in the World axes. The camera prim, represented in the world axes, is shown in the figure below.

_images/camera_frames_v2.002.png

USD Axes

In the computer graphics community, the USD convention is used. The USD axes uses the +Y up, -Z forward convention. In an Isaac Sim application, the Property panel displays the poses of objects in the USD stage. The poses of all objects in the stage are displayed in the world axes, with the exception of camera prims, which is displayed in the +Y up, -Z forward convention. Therefore, this convention is referred to as USD Axes in the context of camera prims. The camera prim, represented in the USD axes convention, is shown in the figure below.

_images/camera_frames_v2.001.png

ROS Axes

The ROS axes uses the -Y up, +Z forward convention. Therefore, any camera data including transforms published to ROS ( ROS Cameras ) or ROS2( ROS2 Cameras ) will be represented in this convention. The camera prim, represented in the ROS axes convention, is shown in the figure below.

_images/camera_frames_v2.003.png

Transforms Between These Frames

For observing poses of camera prims in the proper axes convention, see the Camera Inspector tutorial.