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Glitch/inconsistency detection in navigation data
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Mogens Beltoft
science forum beginner


Joined: 28 Jun 2006
Posts: 1

PostPosted: Wed Jun 28, 2006 3:05 pm    Post subject: Re: Glitch/inconsistency detection in navigation data Reply with quote

Ulrich Bangert wrote:
Quote:
Hello JF Mezei,

Ok. fair enough. But that still leaves the requirement that the user
know about the type of data that he has to process, the types of
irregularities which must be retained, and those that can be removed
because this will be needed to decide on the window size. And one also
need to know how the data was collected.

Agreed!

of stray points. With "auto" track recording, chances are very good that
the GPS would record a point at the turnoff, one point at the stop for
water, and again a point once the car gets back to main road and turns
back into the normal direction.

I am not sure if i interprete the term "auto track recording" in the right
way. Perhaps it is even a "standard" term in navigation that i am not aware
of (I have seen the question for outlier detection purely from a
mathematical point of view). But if it is some kind of "event driven" track
recording you are of course right that the proposed algorithm can not handle
data acquired in this way because some frontend entity has already made the
decision what an event is and what not and has missed to acquire the
"surrounding data" that are necessary for the algorithm.

I read somewhere, that some GPS units use a boundary and time check when
recording track points in auto mode.

It went something like this:

If the new sampled track point n is outside the "road" defined by track
points n-1 and n-2 plus a margin to each side of the line n-2 to n-1, or
the unit has not recorded a track point for "this long", then record
track point n.

/Mogens
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JF Mezei
science forum beginner


Joined: 26 Jun 2006
Posts: 6

PostPosted: Wed Jun 28, 2006 7:13 pm    Post subject: Re: Glitch/inconsistency detection in navigation data Reply with quote

Mogens Beltoft wrote:
Quote:
If the new sampled track point n is outside the "road" defined by track
points n-1 and n-2 plus a margin to each side of the line n-2 to n-1, or
the unit has not recorded a track point for "this long", then record
track point n.


Change in speed also causes a track point to be recorded on sime Garmin
units. And I think that change in heading also does. I don't think
Garmin ever documented the algorythm.
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Steve Underwood
science forum beginner


Joined: 26 May 2005
Posts: 7

PostPosted: Thu Jun 29, 2006 1:44 am    Post subject: Re: Glitch/inconsistency detection in navigation data Reply with quote

Jerry Avins wrote:
Quote:
JF Mezei wrote:

...

So one must really understand the "event" as well as how the data was
recorded for that event before starting to process such data and
eliminate points judged to be "bad".

One must always understand data in order to analyze and interpret it
meaningfully. Believing otherwise is like believing that someone can
manage a business without understanding its nature.

Tell that to an MBA. :-)

You are quite right. When I asked what kind of nav system this is, there
was no response. All the discussion has been about hypothetical
something or others, rather than real world improvement of specific
problems in the data.

Steve
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Rune Allnor
science forum beginner


Joined: 03 May 2005
Posts: 18

PostPosted: Thu Jun 29, 2006 3:26 am    Post subject: Re: Glitch/inconsistency detection in navigation data Reply with quote

Steve Underwood wrote:
Quote:
Jerry Avins wrote:
JF Mezei wrote:

...

So one must really understand the "event" as well as how the data was
recorded for that event before starting to process such data and
eliminate points judged to be "bad".

One must always understand data in order to analyze and interpret it
meaningfully. Believing otherwise is like believing that someone can
manage a business without understanding its nature.

Tell that to an MBA. :-)

You are quite right. When I asked what kind of nav system this is, there
was no response. All the discussion has been about hypothetical
something or others, rather than real world improvement of specific
problems in the data.

Steve

My apologies for that, Steve. These *are* real-world data from
real-world
systems, but as I don't know exactly where the limits go for corporate
"hush-hush" I'll rather play it safe for now. And, of course, I can
guess
but I don't necessarily know the important details.

No offence to you or any other. I saw a way of doing things and I
wanted
to know what the alternatives, preferably commercially available, are.
As
there seems to be no canned solution available, I'll probably have to
program some Kalman filters myself and play with them until I get a
sense for how these things work and how to incorporate the various
ideas.

Rune
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