6.3 Coordinate systems
In ASAM OpenSCENARIO, the following coordinate system types are defined:

A coordinate system that consists of three orthogonal directions associated with X, Y, and Z axes and a coordinate origin where axes meet, defines the righthanded Cartesian coordinate system. It is compliant with the ISO 8855:2011 [11] definition. Orientation of road objects is expressed extrinsically by the heading (yaw), pitch, and roll angles derived from the sequence of rotations in the order: Zaxis, then Yaxis, then Xaxis. The positive rotation is assumed to be counterclockwise ("righthand rule", see Figure 5):
Figure 5. Heading, pitch, and roll angle in an ISO 8855:2011 compliant coordinate system 
A roadbased coordinate system that consists of two coordinate axes associated with the reference line of the corresponding road (saxis) and the direction orthogonal to it (taxis) and pointing leftwards. The definition of the s and taxes depends on the reference part of the road in use (see Figure 6):
Figure 6. Roadbased s/tcoordinate system with origin at the beginning of the road 
A coordinate system associated with positions on the earth and defined by the corresponding terrestrial reference system (geodetic datum) in use.
These coordinate system types are referenced to create the following coordinate systems:
6.3.1. World coordinate system (X_{w}, Y_{w}, Z_{w})
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 superelevation, or a lateral road shape profile).
6.3.2 Road coordinate system (s/t)
To every road specified in the road network definition document (external to ASAM OpenSCENARIO), there is a s/ttype coordinate system assigned. The road reference line defines the saxis belonging to the (X,Y)plane of the world coordinate system. The shape of the saxis line is flat and determined by the geometry of the road projected on the (X,Y)plane (Zcoordinates equal to 0). The origin of scoordinates are fixed at the beginning of the road reference line and not affected by an elevation of the road (its inclination in the sdirection).
In contrast, multiple taxes can be defined along the saxis. Each taxis points orthogonally leftwards to the saxis direction and originates on the saxis at the point with the concerned scoordinate. All taxes lie on the surface which is derived from the road surface as if its elevation were not considered. Therefore, taxes adopt a lateral slope of the road as they are oriented coplanar to the road surface. As the consequence, tcoordinates are not affected by a superelevation of the road.
The following constraints are defined:

It is assumed the saxis line has a smooth shape (no leaps nor kinks).

Being twodimensional by its nature, the Road coordinate system does not define any vertical positioning. This means positions, specified with (s/t)coordinates, are on the road surface.

Both s and tcoordinates are applicable within boundaries of the respective road only.

In the case of multiple chained roads, each road defines its own saxis.

In the case of roads with a complex lateral profile (for example, uneven surface), applicability and conversion of s/tcoordinates into other coordinate systems might appear problematic or even impossible.
6.3.3 Lane coordinate System (s/t)
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/ttype coordinate system assigned. The lane’s center line defines the saxis going in the middle between lane’s side boundaries throughout the whole lane section in the direction of the road’s saxis. The shape of the saxis line is determined by the geometry of the respective lane. The saxis lies on the road surface and therefore takes into account an elevation of the road (its inclination in the sdirection). The origin of scoordinates is fixed to the beginning of the lane section.
In contrast, multiple taxes can be defined along the saxis. Each taxis points orthogonally leftwards to the saxis direction and originates on the saxis at the point with the concerned scoordinate. All taxes 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:

It is assumed the saxis line has a smooth shape (no leaps nor kinks).

Being twodimensional by its nature, the Lane coordinate system does not define any vertical positioning. This means positions, specified with (s/t)coordinates, are on the road surface.

Scoordinates are applicable within the length of the respective lane section only.

Tcoordinates are applicable within the width of the respective road only.

In the case, a road contains multiple lane sections, each lane section defines its own set of lanes with their own saxes.

In the case of roads with a complex lateral profile (for example, uneven surface), applicability and conversion of s/tcoordinates into other coordinate systems might appear problematic or even impossible.
6.3.4. Vehicle coordinate system (X_{v}, Y_{v}, Z_{v})
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.
6.3.5. Pedestrian / MiscObject coordinate system (X_{p/m} , Y_{p/m} , Z_{p/m})
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 Zaxis 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.
6.3.6 Trajectory coordinate system (s/t)
To every trajectory specified within the scenario, there is a s/ttype 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 saxis course and shape. The origin of scoordinates is fixed to the beginning of the trajectory line which can go through multiple chained roads.
In contrast, multiple taxes can be defined along the saxis. Each taxis points orthogonally leftwards to the saxis direction and originates on the saxis at the point with the concerned scoordinate. All taxes 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:

Being twodimensional by its nature, the Trajectory coordinate system does not define any vertical positioning. This means positions, specified with (s/t)coordinates, are on the road surface.

Scoordinates are applicable within the length of the respective trajectory line only.

Tcoordinates are applicable within boundaries of the respective road only.

If a trajectory line has a polyline shape, taxes are undefined at points where the line has sharp kinks.

In the case of roads with a complex lateral profile (for example, uneven surface), applicability and conversion of s/tcoordinates into other coordinate systems might appear problematic or even impossible.
6.3.7 Geographic coordinate system (latitude, longitude, altitude)
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/Zaxis 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.
6.3.8 Positioning
ASAM OpenSCENARIO provides various ways to position or localize instances of Entity
acting in the scenario:

Absolute in the world coordinate system

Absolute/relative in the geographic coordinate system

Relative to another
Entity

Absolute/relative in the road coordinate system

Absolute/relative in the lane coordinate system

Relative to a
Route

Relative to a
Trajectory