Read terrain texture

Hello,

I am using the WheeledVehicule object and I am trying to detect the material/texture that the wheel is touching on the terrain. I can see that in the updateWheelParticles function, it is trying to do similar detection to change the color of the dust particules emitted by the wheels. It doesn't seem to be implemented. In fact, I want to know if I am on the grass, dirt or gravel/rock.

Can anyone point me to the location of where I can get this information in the engin? That would really help me out.

Thanks.