Re: GPS Ideas
- From: "David L. Jones" <altzone@xxxxxxxxx>
- Date: 8 Jun 2006 02:53:16 -0700
Abstract Dissonance wrote:
"David L. Jones" <altzone@xxxxxxxxx> wrote in message
news:1149752899.873010.309430@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Abstract Dissonance wrote:
I was reading some stuff today about GPS and had a few ideas. I'm curious
as
to if anyone things they have any practicality. I am by no means an
expert
on GPS and basically this is my first time even reading about some of the
specs and stuff. I did take several courses in physics several years ago
by
I have forgotten most, if not all of what I have learned. These are just
ideas and I am not saying they will work or even make sense... just
trying
to get some feed back. (note, everyone is non-relativistic for
simplicity)
I was thinking that one could attach to each satellites two frequencies
to
transmit on. This might help in solving the problem of the speed of light
changing due to the different mediums that it transmits through.
The data that the satellite transmits would include the distance from
itself
to all other satellites and to a reference on the ground.
The idea for the different frequencies is to somehow build up a
differential
method of dealing with the change in the speed of light as it passes from
the transmitter to the receiver. I'm not sure if it will work but I was
thinking that, say, if satellite A transmits the signal on frequency X
and
frequency Y that one might be able to remove the changes in the speed of
light through the different mediums because it will effect both signals
the
same amount. Not sure if this would lead to something worthwhile though.
Basically it would seem that one could compute the dispersion due to the
medium between the transmiter and receiver to "repair" the distance
computed. Maybe there are other ways to do this too by using only one
signal and by using some modulation method.
By including the distances(and maybe positions too) from all the
satellites
from each other, which are able to computed in a vacuum(I think, not sure
if
it will go through the ionosphere but maybe the method above could work
too). This might not be practical as the satellites would have to send
signals to each other too and some power would be wasted.
It would seem that by knowing the complete geometry of all the satellites
one could use that information to compute a more accurate location of the
GPS receiver. Basically all the information to find the location on
earth
would be sent by just one signal. Since the receiver would be getting
atleast three signals(or six) and a series of data that should be
identical
except for the computed distances to the reciever from each of the 3
satellites, it could compute errors in the distances and possibly use
statistics to increase the accuracy of the data. One could also calcuate
angles for whatever reason too. By having ground facillaties included,
which
would essentially be "fixed" satellites, would could tie everything
together. i.e., angles could be computed from a reference point, say the
north and south poles. One could possibly, say, know how far they are
from
the polar axis and such... which at this point I think at this point one
has
to reply on "maps" to figure things like that out.
Not sure if that makes sense or would work but just an idea.
Thanks,
Jon
GPS works fine just the way it is.
A $100 receiver will get you 5m general accuracy, a more expensive
survey or military model will get you down to the cm range.
In the US you guys have WAAS which gets you even better accuracy.
I'd suggest taking up Geocaching, the fresh air might do you some good!
:->
In the GPS Specs I just read it said that the best is ~20meters, with waas
its like 5 and with differential GPS its about 1-3 meters.
That's what the specs say for instantaneous accuracy.
But in practice you can easily get <5m accuracy with even the cheapest
GPSr. This is how the sport of Geocaching is able to work. Geocachers
routinely get 5m or better accuracy between different receivers at
different times of day and year with some basic averaging techniques.
10m error is generally considered "out by a lot". That's without WAAS
too which we don't have here in Australia.
http://en.wikipedia.org/wiki/NAVSTAR
While I'm sure thats a tremendous amount of resolution for such long
distances surely any improvement would be a good thing? (not that I am
saying I can improve it but mainly I was just wondering about the
feesibility of my ideas).
Also I'm sure that if one wants to increase the accuracy then it requires
more expensive equipment and perhaps larger equipment?
Yes, if you spend (a lot) more money on a receiver and you get cm
accuracy. The capability is already there in the current system.
Larger?, maybe a bit, but my GPSr that fits on my wrist and gets 5m is
good enough for most normal purposes.
Dave :)
.
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