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Unread 13-01-2004, 15:32
Dave Flowerday Dave Flowerday is offline
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Re: Misnomers - Please Don't Use

Quote:
Originally Posted by Chris Hibner
Rarely do I stand up on a soapbox and preach, but I'm going to do so here:
You might want to get off that soapbox, Chris. You're right that dead reckoning came from deduced reckoning, but "deduced reckoning" seems to be widely accepted to mean "determining one's position using a starting point, and adding distance traveled at a certain heading." Merriam-Webster defines dead reckoning as:
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1 : the determination without the aid of celestial observations of the position of a ship or aircraft from the record of the courses sailed or flown, the distance made, and the known or estimated drift
2 : GUESSWORK
Are you not navigating without the aid of celestial observations (or in our case, a fixed reference point) using the record of courses sailed or flown (again, in our case, knowing your heading and distance travelled in that direction)?

After reading a good deal about the subject last year, I came to the conclusion that our positioning system was indeed dead reckoning, and that generally the crowd on Chief Delphi used the term incorrectly to mean dead reckoning based on timing information only.

I think this excerpt explains it well (from this web site):
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First, a definition is in order. Dead reckoning is the process of estimating the position of an airplane or ship based solely on speed and direction of travel and time elapsed since the last known position (or fix). So all you need to figure out approximately where you are is an airspeed indicator or log or other measure of speed, a clock or watch, and a compass. Dead reckoning stands in contrast to pilotage (navigation by visible landmarks) and celestial navigation (navigation by reference to stars or other heavenly bodies). Since the development of radio technology, various forms of electronic navigation have also been developed, the best known of which is the satellite-based Global Positioning System. Navigating by external reference points is more accurate, but dead reckoning is the fallback when all else fails.
Your navigation system, like ours, wasn't navigating by any external reference, right?
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Do you KNOW where you are? NO!!! You only have an approximate idea via deduction.
Does your navigation system really know where it is? I don't think so. If your measurement wheel slips, your positioning system will think it's somewhere it's not - because you DEDUCED your position knowing a direction and distance traveled. Your robot cannot know with certainty that it actually reached it's destination without being able to observe something external - visually inspecting it's surroundings, using GPS, having someone else observe it and tell it that it's reached it's destination, etc.