Question regarding Ego-vehicle velocities (lateral and longitudinal)

[danielaDESM]

Hi!
I hope yo can help me to understand the following:

I would like to get ground truth data of the velocities in x,y,z w.r.t the coordinate system of the ego vehicle. So far I have only seen the vehicle.get_velocity(), but those are computed w.r.t the coordinate system of the map .
For instance, if the car is driving along the Y- axis in the map, vehicle.get_velocity().x would give me a value close to zero (assuming the car does not do any turns or lane change) and vehicle.get_velocity().y would have a certain value.
But from the perspective of the car, according to the definition of it's coordinate system (x-fwd, y-right, z-up), the velocity would show up in the x axis and close to zero in the y-axis.
I am estimating velocities through the registration of point clouds and I want to know how good I perform.
I would highly appreciate your help.