6.3 Coordinate systems

Coordinate system of type (X, Y, Z) fixed in the inertial reference frame of the simulation environment, with X_w and Y_w axes parallel to the ground plane and Z_w axis pointing upward.

Neither origin nor orientation of the world coordinate system are defined by the ASAM OpenSCENARIO standard. If a road network is referenced from a scenario, the world coordinate system is aligned with the inertial coordinate system present in this description (in particular, the Z_w-coordinate is assumed to consider a road elevation, an entire road super-elevation, or a lateral road shape profile).

To every road specified in the road network definition document (external to ASAM OpenSCENARIO), there is a s/t-type coordinate system assigned. The road reference line defines the s-axis belonging to the (X,Y)-plane of the world coordinate system. The shape of the s-axis line is flat and determined by the geometry of the road projected on the (X,Y)-plane (Z-coordinates equal to 0). The origin of s-coordinates are fixed at the beginning of the road reference line and not affected by an elevation of the road (its inclination in the s-direction).

In contrast, multiple t-axes can be defined along the s-axis. Each t-axis points orthogonally leftwards to the s-axis direction and originates on the s-axis at the point with the concerned s-coordinate. All t-axes lie on the surface which is derived from the road surface as if its elevation were not considered. Therefore, t-axes adopt a lateral slope of the road as they are oriented coplanar to the road surface. As the consequence, t-coordinates are not affected by a superelevation of the road.

The following constraints are defined:

To every lane specified in a lane section of a road (the road network definition document is external to ASAM OpenSCENARIO), there is a s/t-type coordinate system assigned. The lane’s center line defines the s-axis going in the middle between lane’s side boundaries throughout the whole lane section in the direction of the road’s s-axis. The shape of the s-axis line is determined by the geometry of the respective lane. The s-axis lies on the road surface and therefore takes into account an elevation of the road (its inclination in the s-direction). The origin of s-coordinates is fixed to the beginning of the lane section.

In contrast, multiple t-axes can be defined along the s-axis. Each t-axis points orthogonally leftwards to the s-axis direction and originates on the s-axis at the point with the concerned s-coordinate. All t-axes lie on the surface of the road and therefore adopt a lateral slope profile and an elevation of the road.

The following constraints are defined:

The vehicle axis system of type (X, Y, Z), as defined in ISO 8855:2011 [11], is fixed in the reference frame of the vehicle sprung mass. The X_v axis is horizontal and forwards with the vehicle at rest. The X_v axis is parallel to the vehicle’s longitudinal plane of symmetry. The Y_v axis is perpendicular to the vehicle’s longitudinal plane of symmetry and points left. The Z_v axis points upward.

In ASAM OpenSCENARIO, the origin of this coordinate system is derived by projecting the center of the vehicle’s rear axis to the ground plane at neutral load conditions. The origin remains fixed to the vehicle sprung mass, as illustrated in Figure 7.

The axis system for a pedestrian (subscript p) or a miscellaneous object (subscript m) is fixed in the reference frame of the object’s bounding box. The X axis is horizontal and normal to the object’s front plane. The Y axis is horizontal, perpendicular to X, and points to the left. The Z-axis points upward.

The origin of this coordinate system is derived from the geometrical center of the object’s bounding box under neutral load conditions (if applicable) projected onto the ground plane.

To every trajectory specified within the scenario, there is a s/t-type coordinate system assigned. The trajectory is deemed as an imaginary spatial directed line ("trajectory line") on the road surface indicating a movement path. The geometry of the trajectory line defines the s-axis course and shape. The origin of s-coordinates is fixed to the beginning of the trajectory line which can go through multiple chained roads.

In contrast, multiple t-axes can be defined along the s-axis. Each t-axis points orthogonally leftwards to the s-axis direction and originates on the s-axis at the point with the concerned s-coordinate. All t-axes lie on the surface of the road and therefore adopt a lateral slope profile and an elevation of the road.

The following constraints are defined:

ASAM OpenSCENARIO accepts position coordinates expressed in spherical geographic coordinate systems as longitude, latitude, and altitude. Interpretation of geographic coordinates might depend on the reference geoid model (datum) used in the geographic coordinate system and is therefore external to ASAM OpenSCENARIO.

The world coordinate system is considered the projected coordinate system compatible with the ENU (East, North, Up) convention of the X/Y/Z-axis directions and is derived from the used geographic coordinate system that is based on the applied geoid model. The (X,Y)-plane of the world coordinate system is assumed to be a local tangent plane in relation to the surface of the reference geoid model.

If coordinates of positions are derived from the geographic coordinate system, the road network definition shall specify the map projection system type involved and provide its mandatory parameters.

ASAM OpenSCENARIO provides various ways to position or localize instances of Entity acting in the scenario: