Class: Class():Sensor(),rsensor(),rvelocity(){}

Dear c++ gurus, i have thk all over wat is means by the following hightlighted text, but not understood, can anyone explain to me what do they mean? or how do they function?

Code:

      class RotationSensor : public Sensor {
      public:

      RotationSensor(const Port port, int position = 0)
           : Sensor((Sensor::Port) port, true),
            rsensor((port == S1) ? ROTATION_1 :
           (port == S2) ? ROTATION_2 :
            ROTATION_3)
   
     #ifdef CONF_DSENSOR_VELOCITY
              ,
             rvelocity((port == S1) ? VELOCITY_1 :
                          (port == S2) ? VELOCITY_2 :
                          VELOCITY_3)
     #endif // CONF_DSENSOR_VELOCITY
       {
       on(); //! Turn on tracking of the sensor
       pos(position); //! Set the current position
       }
 
      ..........................................................
       }

How does the following function/run/do/etc?

RotationSensor(...) : Sensor (...), rsensor(...), rvelocity(...)
{
on();
pos(position);
}

wat does this block of codes represent? or do? or how it function?

Thanks guru.