[FoRK] Has anyone of you ever experimented with a GPS receiver?

Russell Turpin deafbox at hotmail.com
Tue Jul 20 07:59:58 PDT 2004


I've used them quite a bit. GPS generally has
a resolution of dozens of yards in the horizontal
plane. Its resolution in the vertical plane is
worse, at least with most commercial receivers.

Differential GPS will narrow that resolution to
yards, which likely still isn't fine enough. I've
never used a DGPS receiver, so I have no direct
experience with it. These receivers rely on a
fixed basepoint nearby, to refine their
calculations.

With regard to keeping a car on the road, the
larger issue is that a GPS receiver has no way
to determine velocity except by the history
of your past location. For navigating a car,
you'd want not only DGPS, to get current
position, but also a fluxgate compass, to know
your current direction. Sailors have some
experience integrating all of these using a PC,
though I've never gotten into this.

How well do you know the location of the
road? For one road, you can plot this using
DGPS. But in general..? There have been
several marine incidents where boats were
navigated onto reefs or other obstruction,
because their operators were relying solely
on GPS, which did indeed give the boat's
accurate location, but the most recent
survey of the land involved was done using
a sextant ninety years previous. Roads,
sandbars, and cutwaters also get moved. It's
important for navigators to remember the
inherent limitations of a map. ;-)

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