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[DPRG] digital compass in my car went crazy in Canada
Subject: [DPRG] digital compass in my car went crazy in Canada
From: William Crolley
w.crolley at mchsi.com
Date: Thu May 22 08:31:44 CDT 2008
There are two main causes for the variation in compass reading. The easy
one is that the north/south poles do not line up with the north/south
magnetic poles. And the magnetic poles are slowly moving, just to make it
more interesting.
But the variation also changes due to the magnetism of the rocks in the
area. A notorious example is Magnetic Island in Lake Superior where the
iron ore causes the compass to basically point towards the island. Not
good in one of the foggiest parts of the lower 48 states.
William Crolley
> > Don't know if this is related, but I borrowed a Brunton recently
> > from the SMU geology department that had just been used for some
> > field work in Alaska, and I was surprised to find that the correction
> > for magnetic variation pointed almost due east! In Dallas the
> > correction is about 4.5 degrees east, so everything was off
> > significantly until we reset the compass.
>
> Hi David, I noted a reading bias towards east until well south of the
Canadian
> border. So I was heading due S but the compass kept reading SE. I wonder
how
> these devices work in Canada? Maybe they only sell them with a GPS
receiver.
>
> > So Chris, we would love to see an outdoor robot do the DPRG
> > ORC challenges with vision alone, optical flow, terrain mapping,
> > scene recognition or whatever. Lots of builders think that
> > ultimately the whole navigation process might be accomplished
> > visually. But it's not clear how to get from here to there.
> > How are you progressing?
>
> I would love to see the same things too. The last few months have
> been between 70 to 90 hour work weeks. I have been swamped with
> my job.
>
> Here's what I've learned in the last eight months.
>
> You were right - by that I mean the solution to this outdoor
> robot problem. And pretty much the solutions adopted by the DARPA
> challenge robots are also correct. They are all designed with
> practical consideration of current technology.
>
> Statistical methods are not magic. They are necessary when data
> quality is low or when ... theory is inadequate. We just may not
> understand the problem. In this case, statistics may be the only
> tool we have.
>
> Computer vision has many deep limitations. It splits into two main
> areas: data mining and scene registration. The former is about
> classification, clustering and search. The latter is estimating
> geometry. All of this is immature.
>
> Regarding robots - vision tends to have high computational
> complexity. It is far cheaper to use odometry and an IMU instead
> of relying on a bigger computer that can see. I think now that
> vision does make sense for doing things that are otherwise
> impossible without it. So a cruise missile might need to see to
> get really precise terminal guidance. Or a robot on land might
> need to read street signs or look down a road into the far
> distance. But in both cases, vision augments RADAR, LIDAR and
> conventional statistical filtering to improve performance. It's
> not a substitute for traditional approaches.
>
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