Re: GPS thingy?
- From: "B Fuhrmann" <b-fuhrmann-usenet@xxxxxxxxxxxxxxxxxxxxxxxxx>
- Date: Fri, 8 Jul 2005 16:48:07 -0500
"nano" wrote ...
>I saw some of the discussion about GPS mapping or making routes?
> What are those for? Where do you buy them? Can someone explains some
> facts about it to me? Thanks in advance!
Global Positioning Satellite receivers get time and location readings from a
group of satellites at the same time and then use some math to figure where
they are relative to the satellites.
Everything else depends on the features you buy.
A couple of the easiest features is to add is to calculate your speed from
the difference in position over time and to record how far or where you
went. Some of the small units are designed for runners (and skaters) to
wear on our wrists to record your training. There is also one that includes
a heart rate monitor for further training use.
As you get fancier, you can add the ability to add maps to the receiver so
that you can find where you are or to give you directions to get to your
destination.
A coworker just bought a Garmin 18 package for use on trips. It plugs into
a laptop via a USB port. With the full power of a computer tied to the
receiver, you tell it where you want to go and it figures out the route,
announcing turns as you come to them.
The ones you see being commented on here are typically either the wrist
versions or small hand held ones designed for outdoors use. Mine is an
Etrex Vista which is on the high end for the hand helds. It has more memory
so that you can add more maps into it and it has a barometric altimeter so
that the altitude readings are more stable than a standard GPS.
Those of us who are doing mapping with them have additional software (ranges
from free to $130) which can download the data from the GPS and draw it on
the map.
Even though Garmin doesn't publish their data format to upload the map data
a few people have figured it out and created software that lets you create
your own maps that you can load into the GPS for portable use.
Under typical conditions a GPS is accurate within 20-50 feet. I think that
Garmin's estimate of accuracy is optimistic. The readings are taken so that
it improves the accuracy of the position on the surface of the earth and
lets the altitude not be as accurate.
If you are in the south part of the US, you can receive the WAAS signal
which will improve the accuracy. Supposedly that will get you within 3-15
feet for accuracy.
You can also add DGPS (Differential) which with the proper equipment will
get you down to inches.
We have some experimental equipment at work that has an antenna at each end
and DGPS receivers. From the locations of each end of the machine, it can
tell exactly where it is and which way it is pointing. In order to do this,
we have a stationary antenna mounted nearby which transmits what it sees
from each of the satellites so that the ones on the equipment can correct
for errors caused by the radio waves traveling through the atmosphere.
I have ridden in a car that is used for mapping. The stationary antenna was
30 miles away but it was giving us readings that were accurate to within an
inch. The software included calibration for where we wanted to map, shifted
from the antenna. We specified on the ground, just to the right of the
front right tire and used it to map the edges of a road course. The data
was going to be used to draw the course accurately for planning future
competition events.
--
Bill Fuhrmann
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