expected_update_rate

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In: http://wiki.ros.org/navigation/Tutori...

I see this:

"Make sure to set the expected_update_rate parameter for each observation source based on the rate at which the sensor actually publishes. I normally give a fair amount of tolerance here, putting the period for the check at twice what I'd expect, but its nice to receive warnings from navigation when a sensor falls way below its expected rate."

But I can't find expected_update_rate anywhere. Can someone point me at it? Or is that Nav Tuning Guide obsolete, or is there a better one?