🪜Coordinate System

The coordinate system of ROAR_PY follows a right-hand, Z-up system. All rotations follow the right hand rule and the rotation order is XYZ.

The standard units in ROAR_PY are meters(m) and radians(rad).

Very typical representations of coordinate system data are locations np.ndarray with size (3,) with each index representing x,y,z in meters and rotations np.ndarray with size (3,) and each index representing rotation in x,y,z (roll, pitch, yaw) in radians.

We do not impose restrictions on the world coordinate's x and y axis but every implementation of ROAR_PY should have world coordinate's z axis in the direction of the gravity.

However, we ask that any implementation of ROAR_PY should have local coordinates (of any ROAR_PY actor) that has the following property:

1. The x-axis should point in the forward direction of the actor

2. The y-axis should point in the left direction of the actor

3. The z-axis should point in the upward direction of the actor

Below are a few examples of local coordinate systems in ROAR_PY

Robot Dog

The Boston Dynamics Spot SDK coordinate system uses the same coordinate system as ROAR_PY (Credit: Boston Dynamics website)

Carla Vehicle

In ROAR_PY's carla implementation, the X axis is defined to be pointing to the front of the vehicle, the Y axis is pointing to the left of the vehicle, and the Z axis points upwards.

Note that since Carla uses UE4's left handed z-up coordiante system, ROAR_PY converts those coordinates internally. The exact conversion can be found in ROAR_PY's convert_coordinate file

Waypoint

A maneuverable waypoint in ROAR_PY is laid on the exact center of the road, the x axis points in the "forward" direction of the road, y axis points in the "left" direction of the road, and z axis points in the "up" direction of the road. The width attribute defines how much the road spans (in meters) at the exact lateral location.