How to make Ray sensor ignore body of the robot?

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Is there any way how to define which models should not collide with the laser rays? I need to detect obstacles very close to the robot, but sometimes the robot parts get in way of the sensor and the closest distance is the distance to the robot part instead of the obstacle. I'm not aiming for a realistic simulation of laser sensor with this particular sensor. I just need the distances from the surrounding models to the robot.