Vehicle reference point fixed to vehicle sprung mass
The definition of the vehicle coordinate system in 6.3.4. specifies that the origin of the vehicle coordinate system is fixed to the vehicle sprung mass. The origin is defined to be at the ground projection of the rear axle center at neutral load conditions. This means that the origin could very well be below ground in the case of higher load conditions. Is this intended? I understand that this comes from ISO 8855 but the reference points specified in there are probably more oriented towards vehicle-internal stuff and not - as in the case of OpenSCENARIO - used for placement of vehicles in a "bigger world" or similar. Also, as far as I see, in the ISO they don't use ground projections.
6.3.4. Vehicle coordinate system (Xv, Yv, Zv)
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 Xv axis is horizontal and forwards with the vehicle at rest. The Xv axis is parallel to the vehicle’s longitudinal plane of symmetry. The Yv axis is perpendicular to the vehicle’s longitudinal plane of symmetry and points left. The Zv 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.