Value of sensor_msgs/Range field of view for ultrasound sensors.

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I've a possible answer for my own question for the use with the range sensor layer:

1. The sensor SRF05 has a max range of 6m
2. Using this max range of 6m with a high angle like 30 deg will result in a relative small object, e.g. a bottle 5m away to generate a big obstacle in the costmap. This breaks navigation.
3. This is the reason why I want to use the sensor in only a small range* (currently 0.5m).
4. Which leads to the following answer: In close range the field of view (fov) is nearly constant and in practice does not matter, because if two cells (low fov) or four cells (high fov) are marked occupied in front of a robot will both result in the same planner strategy: Rotate until path is clear**.

Warning: Limiting the max range of a range sensor without adjusting the range (e.g. max_range=0.5, range=0.567) will result in obstacles not getting removed from the range layer sensor. So be sure to clip all values > max_range to max_range. * Assuming nonholonomic robots with a reasonable size.